diff --git a/src/rez/rex.py b/src/rez/rex.py
index 9eccdfda2..aa25707d6 100644
--- a/src/rez/rex.py
+++ b/src/rez/rex.py
@@ -277,7 +277,8 @@ def _fn(str_):
                 # in a request string which python on windows will expand
                 # regardless if the user exists or not
                 matches = re.findall(r"[\\/]?", str_)
-                matches = list(set(matches)).remove("")
+                matches = list(set(matches))
+                matches.remove("")
                 if matches:
                     return os.path.expanduser(str_)
                 else:
diff --git a/src/rez/shells.py b/src/rez/shells.py
index 4dec45245..2c2fe5955 100644
--- a/src/rez/shells.py
+++ b/src/rez/shells.py
@@ -139,8 +139,7 @@ def get_syspaths(cls):
     def __init__(self):
         self._lines = []
         self.settings = config.plugins.shell[self.name()]
-        self.env_sep_map = self._get_env_sep_map()
-        self.validate_env_sep_map()
+        self.env_sep_map = self._shell_env_seps()
 
     def _global_env_seps(self):
         setting = self.env_sep_map_setting
@@ -148,18 +147,20 @@ def _global_env_seps(self):
         return value
 
     def _shell_env_seps(self):
+        self.validate_env_sep_map()
         shell = self.name()
         setting = self.shell_env_sep_map_setting
         values = config.get(setting, {})
         value = values.get(shell, {})
         return value
 
-    def _get_env_sep_map(self):
+    def validate_env_sep_map(self):
         """
-        Get a dict of environment variable names to path separators.
+        Validate environment path separator settings.
         """
-        if getattr(self, "env_sep_map", None):
-            return self.env_sep_map
+        # Return early if validation is disabled.
+        if not config.warn("shell_startup"):
+            return
 
         global_env_seps = self._global_env_seps()
         shell_env_seps = self._shell_env_seps()
@@ -180,11 +181,6 @@ def _get_env_sep_map(self):
                         pathsep,
                     )
 
-        return shell_env_seps
-
-    def validate_env_sep_map(self):
-        pass
-
     def _addline(self, line):
         self._lines.append(line)