diff --git a/spine_engine/jumpster.py b/spine_engine/jumpster.py
index ce55e09..117437d 100644
--- a/spine_engine/jumpster.py
+++ b/spine_engine/jumpster.py
@@ -65,7 +65,7 @@ def __init__(self, event_type, item_name, direction, **kwargs):
 
 
 class Failure(BaseException):
-    """A failure"""
+    """Item execution stopped by failure or user interruption."""
 
 
 class Output:
@@ -80,7 +80,7 @@ def __init__(self, item_finish_state):
 
 class JumpsterThreadError(Exception):
     """An exception has occurred in one or more of the threads jumpster manages.
-    This error forwards the message and stack trace for all of the collected errors.
+    This error forwards the message and stack trace for all the collected errors.
     """
 
     def __init__(self, *args, **kwargs):
@@ -251,7 +251,6 @@ def execute(self):
                     empty_iters.append(key)
                 except StopIteration:
                     empty_iters.append(key)
-                    # TODO: Anything about loops?
             # clear and mark complete finished iterators
             for key in empty_iters:
                 del active_iters[key]
@@ -259,9 +258,7 @@ def execute(self):
         if errs:
             raise JumpsterThreadError(
                 "During multithread execution errors occurred in threads:\n{error_list}".format(
-                    error_list="\n".join(
-                        ["In thread {tid}: {err}".format(tid=tid, err=err.to_string()) for tid, err in errs.items()]
-                    )
+                    error_list="\n".join([f"In thread {tid}: {err.to_string()}" for tid, err in errs.items()])
                 ),
                 thread_error_infos=list(errs.values()),
             )
@@ -338,6 +335,7 @@ def execute_step_in_thread(step, errors):
 
     Args:
         step (Step): step to execute
+        errors (dict): mapping from thread id to error info
     """
     event_queue = queue.Queue()
     thread = threading.Thread(target=_do_execute_step_in_thread, args=(event_queue, step))
@@ -394,4 +392,4 @@ def _do_execute_step_in_thread(event_queue, step):
             ThreadSystemErrorEvent(tid=tid, error_info=serializable_error_info_from_exc_info(sys.exc_info()))
         )
     except Failure:
-        pass
+        event_queue.put(JumpsterEvent(JumpsterEventType.STEP_FAILURE, step.item_name, step.direction))
diff --git a/spine_engine/project_item/connection.py b/spine_engine/project_item/connection.py
index 64d071c..0f28bed 100644
--- a/spine_engine/project_item/connection.py
+++ b/spine_engine/project_item/connection.py
@@ -589,8 +589,10 @@ def from_dict(cls, connection_dict):
 class Jump(ConnectionBase):
     """Represents a conditional jump between two project items."""
 
+    _DEFAULT_CONDITION = {"type": "python-script", "script": "exit(1)", "specification": ""}
+
     def __init__(
-        self, source_name, source_position, destination_name, destination_position, condition={}, cmd_line_args=()
+        self, source_name, source_position, destination_name, destination_position, condition=None, cmd_line_args=()
     ):
         """
         Args:
@@ -598,11 +600,11 @@ def __init__(
             source_position (str): source anchor's position
             destination_name (str): destination project item's name
             destination_position (str): destination anchor's position
-            condition (dict): jump condition
+            condition (dict, optional): jump condition
+            cmd_line_args (Iterable of str): command line arguments
         """
         super().__init__(source_name, source_position, destination_name, destination_position)
-        default_condition = {"type": "python-script", "script": "exit(1)", "specification": ""}
-        self.condition = condition if condition else default_condition
+        self.condition = condition if condition is not None else self._DEFAULT_CONDITION
         self._resources_from_source = set()
         self._resources_from_destination = set()
         self.cmd_line_args = list(cmd_line_args)
diff --git a/spine_engine/project_item/executable_item_base.py b/spine_engine/project_item/executable_item_base.py
index 272ff0d..878bf1a 100644
--- a/spine_engine/project_item/executable_item_base.py
+++ b/spine_engine/project_item/executable_item_base.py
@@ -10,10 +10,7 @@
 # this program. If not, see <http://www.gnu.org/licenses/>.
 ######################################################################################################################
 
-"""
-Contains ExecutableItem, a project item's counterpart in execution as well as support utilities.
-
-"""
+""" Contains ExecutableItem, a project item's counterpart in execution as well as support utilities. """
 from hashlib import sha1
 from pathlib import Path
 from ..utils.helpers import ExecutionDirection, ItemExecutionFinishState, shorten
@@ -28,6 +25,7 @@ def __init__(self, name, project_dir, logger, group_id=None):
             name (str): item's name
             project_dir (str): absolute path to project directory
             logger (LoggerInterface): a logger
+            group_id (str, optional): execution group identifier
         """
         self._name = name
         self._project_dir = project_dir
diff --git a/spine_engine/spine_engine.py b/spine_engine/spine_engine.py
index 8fe6b61..68d5175 100644
--- a/spine_engine/spine_engine.py
+++ b/spine_engine/spine_engine.py
@@ -101,7 +101,6 @@ def __init__(
         Raises:
             EngineInitFailed: Raised if initialization fails
         """
-        super().__init__()
         self._queue = mp.Queue()
         if items is None:
             items = {}
@@ -109,7 +108,7 @@ def __init__(
         if execution_permits is None:
             execution_permits = {}
         self._execution_permits = execution_permits
-        connections = list(map(Connection.from_dict, connections))  # Deserialize connections
+        connections = list(map(Connection.from_dict, connections))
         project_item_loader = ProjectItemLoader()
         self._executable_item_classes = project_item_loader.load_executable_item_classes(items_module_name)
         required_items = required_items_for_execution(
@@ -137,8 +136,11 @@ def __init__(
         self._item_names = list(self._dag)  # Names of permitted items and their neighbors
         if jumps is None:
             jumps = []
-        self._jumps = list(map(Jump.from_dict, jumps))
-        validate_jumps(self._jumps, self._dag)
+        else:
+            jumps = list(map(Jump.from_dict, jumps))
+        items_by_jump = _get_items_by_jump(jumps, self._dag)
+        self._jumps = filter_unneeded_jumps(jumps, items_by_jump, execution_permits)
+        validate_jumps(self._jumps, items_by_jump, self._dag)
         for x in self._connections + self._jumps:
             x.make_logger(self._queue)
         for x in self._jumps:
@@ -275,10 +277,11 @@ def _get_event_stream(self):
         self._thread.start()
         while True:
             msg = self._queue.get()
-            yield msg
             if msg[0] == "dag_exec_finished":
                 break
+            yield msg
         self._thread.join()
+        yield msg
 
     def answer_prompt(self, prompter_id, answer):
         """Answers the prompt for the specified prompter id."""
@@ -760,14 +763,25 @@ def _validate_dag(dag):
         raise EngineInitFailed("DAG contains unconnected items.")
 
 
-def validate_jumps(jumps, dag):
+def filter_unneeded_jumps(jumps, items_by_jump, execution_permits):
+    """Drops jumps whose items are not going to be executed.
+
+    Args:
+        jumps (Iterable of Jump): jumps to filter
+        items_by_jump (dict): mapping from jump to list of item names
+        execution_permits (dict): mapping from item name to boolean telling if its is permitted to execute
+    """
+    return [jump for jump in jumps if all(execution_permits[item] for item in items_by_jump[jump])]
+
+
+def validate_jumps(jumps, items_by_jump, dag):
     """Raises an exception in case jumps are not valid.
 
     Args:
         jumps (list of Jump): jumps
+        items_by_jump (dict): mapping from jump to list of item names
         dag (DiGraph): jumps' DAG
     """
-    items_by_jump = _get_items_by_jump(jumps, dag)
     for jump in jumps:
         validate_single_jump(jump, jumps, dag, items_by_jump)
 
@@ -777,7 +791,7 @@ def validate_single_jump(jump, jumps, dag, items_by_jump=None):
 
     Args:
         jump (Jump): the jump to check
-        jumps (list of Jump): all jumps in dag
+        jumps (list of Jump): all jumps in DAG
         dag (DiGraph): jumps' DAG
         items_by_jump (dict, optional): mapping jumps to a set of items in between destination and source
     """
diff --git a/spine_engine/utils/helpers.py b/spine_engine/utils/helpers.py
index 1d95a1d..1d840de 100644
--- a/spine_engine/utils/helpers.py
+++ b/spine_engine/utils/helpers.py
@@ -405,7 +405,7 @@ def make_connections(connections, permitted_items):
         list of Connection: List of permitted Connections or an empty list if the DAG contains no connections
     """
     if not connections:
-        return list()
+        return []
     connections = connections_to_selected_items(connections, permitted_items)
     return connections
 
@@ -433,10 +433,10 @@ def dag_edges(connections):
     Returns:
         dict: DAG edges. Mapping of source item (node) to a list of destination items (nodes)
     """
-    edges = dict()
+    edges = {}
     for connection in connections:
         source, destination = connection.source, connection.destination
-        edges.setdefault(source, list()).append(destination)
+        edges.setdefault(source, []).append(destination)
     return edges
 
 
diff --git a/tests/project_item/test_connection.py b/tests/project_item/test_connection.py
index a98bda5..4d1f812 100644
--- a/tests/project_item/test_connection.py
+++ b/tests/project_item/test_connection.py
@@ -11,11 +11,12 @@
 ######################################################################################################################
 """ Uni tests for the ``connection`` module. """
 import os.path
+import pathlib
 from tempfile import TemporaryDirectory
 import unittest
 from unittest.mock import Mock
 from spine_engine.project_item.connection import Connection, FilterSettings, Jump
-from spine_engine.project_item.project_item_resource import database_resource
+from spine_engine.project_item.project_item_resource import LabelArg, database_resource, file_resource
 from spinedb_api import DatabaseMapping, import_alternatives, import_entity_classes, import_scenarios
 from spinedb_api.filters.scenario_filter import SCENARIO_FILTER_TYPE
 
@@ -169,6 +170,31 @@ def test_counter_passed_to_condition(self):
         jump.make_logger(Mock())
         self.assertTrue(jump.is_condition_true(23))
 
+    def test_command_line_args_with_whitespace_are_not_broken_into_tokens(self):
+        # Curiously, this test fails when run under PyCharm's debugger.
+        with TemporaryDirectory() as temp_dir:
+            path = pathlib.Path(temp_dir) / "path with spaces" / "file name.txt"
+            condition = {
+                "type": "python-script",
+                "script": "\n".join(
+                    (
+                        "from pathlib import Path",
+                        "import sys",
+                        "if len(sys.argv) != 3:",
+                        "    exit(1)",
+                        f"expected_path = Path(r'{str(path)}').resolve()",
+                        "if Path(sys.argv[1]).resolve() != expected_path:",
+                        "    exit(1)",
+                        "exit(0 if int(sys.argv[2]) == 23 else 1)",
+                    )
+                ),
+            }
+            jump = Jump("source", "bottom", "destination", "top", condition, [LabelArg("arg_label")])
+            resource = file_resource("provider: unit test", str(path), "arg_label")
+            jump.receive_resources_from_source([resource])
+            jump.make_logger(Mock())
+            self.assertTrue(jump.is_condition_true(23))
+
     def test_dictionary(self):
         jump = Jump("source", "bottom", "destination", "top", {"type": "python-script", "script": "exit(23)"})
         jump_dict = jump.to_dict()
diff --git a/tests/test_spine_engine.py b/tests/test_spine_engine.py
index 6228476..44310dc 100644
--- a/tests/test_spine_engine.py
+++ b/tests/test_spine_engine.py
@@ -16,6 +16,7 @@
 Inspired from tests for spinetoolbox.ExecutionInstance and spinetoolbox.ResourceMap,
 and intended to supersede them.
 """
+from functools import partial
 import os.path
 import sys
 from tempfile import TemporaryDirectory
@@ -43,6 +44,11 @@ class TestSpineEngine(unittest.TestCase):
         "script": "\n".join(["import sys", "loop_counter = int(sys.argv[1])", "exit(0 if loop_counter < 2 else 1)"]),
     }
 
+    _LOOP_FOREVER = {
+        "type": "python-script",
+        "script": "\n".join(["exit(0)"]),
+    }
+
     @staticmethod
     def _mock_item(
         name, resources_forward=None, resources_backward=None, execute_outcome=ItemExecutionFinishState.SUCCESS
@@ -97,7 +103,7 @@ def _default_backward_url_resource(url, item_name, successor_name, scenarios=Non
         }
         return resource
 
-    def _run_engine(self, items, connections, item_instances, execution_permits=None, jumps=None):
+    def _create_engine(self, items, connections, item_instances, execution_permits=None, jumps=None):
         if execution_permits is None:
             execution_permits = {item_name: True for item_name in items}
         with patch("spine_engine.spine_engine.create_timestamp") as mock_create_timestamp:
@@ -116,6 +122,10 @@ def make_item(name, direction):
             return item_instances[name][0]
 
         engine.make_item = make_item
+        return engine
+
+    def _run_engine(self, items, connections, item_instances, execution_permits=None, jumps=None):
+        engine = self._create_engine(items, connections, item_instances, execution_permits, jumps)
         engine.run()
         self.assertEqual(engine.state(), SpineEngineState.COMPLETED)
 
@@ -858,6 +868,46 @@ def test_nested_jump_with_inner_self_jump(self):
             expected = 2 * [[[self._default_forward_url_resource(url_fw_b, "b")], []]]
             self._assert_resource_args(item_c.execute.call_args_list, expected)
 
+    def test_stopping_execution_in_the_middle_of_a_loop_does_not_leave_multithread_executor_running(self):
+        item_a = self._mock_item("a")
+        item_b = self._mock_item("b")
+        item_instances = {"a": [item_a, item_a, item_a, item_a], "b": [item_b]}
+        items = {
+            "a": {"type": "TestItem"},
+            "b": {"type": "TestItem"},
+        }
+        connections = [c.to_dict() for c in (Connection("a", "right", "b", "left"),)]
+        jumps = [Jump("a", "right", "a", "right", self._LOOP_FOREVER).to_dict()]
+        engine = self._create_engine(items, connections, item_instances, jumps=jumps)
+
+        def execute_item_a(loop_counter, *args, **kwargs):
+            if loop_counter[0] == 2:
+                engine.stop()
+                return ItemExecutionFinishState.STOPPED
+            loop_counter[0] += 1
+            return ItemExecutionFinishState.SUCCESS
+
+        loop_counter = [0]
+        item_a.execute.side_effect = partial(execute_item_a, loop_counter)
+        engine.run()
+        self.assertEqual(engine.state(), SpineEngineState.USER_STOPPED)
+        self.assertEqual(item_a.execute.call_count, 3)
+        item_b.execute.assert_not_called()
+
+    def test_executing_loop_source_item_only_does_not_execute_the_loop(self):
+        item_a = self._mock_item("a")
+        item_b = self._mock_item("b")
+        item_instances = {"a": [item_a, item_a, item_a, item_a], "b": [item_b, item_b, item_b, item_b]}
+        items = {
+            "a": {"type": "TestItem"},
+            "b": {"type": "TestItem"},
+        }
+        connections = [c.to_dict() for c in (Connection("a", "right", "b", "left"),)]
+        jumps = [Jump("b", "right", "a", "right", self._LOOP_FOREVER).to_dict()]
+        self._run_engine(items, connections, item_instances, execution_permits={"a": False, "b": True}, jumps=jumps)
+        self.assertEqual(item_a.execute.call_count, 0)
+        self.assertEqual(item_b.execute.call_count, 1)
+
     def _assert_resource_args(self, arg_packs, expected_packs):
         self.assertEqual(len(arg_packs), len(expected_packs))
         for pack, expected_pack in zip(arg_packs, expected_packs):