diff --git a/Core/Registry/CompatibilitySorter.cs b/Core/Registry/CompatibilitySorter.cs
index d779cfad3..935bb62ad 100644
--- a/Core/Registry/CompatibilitySorter.cs
+++ b/Core/Registry/CompatibilitySorter.cs
@@ -26,8 +26,8 @@ public class CompatibilitySorter
         /// <param name="dlc">Collection of installed DLCs</param>
         public CompatibilitySorter(GameVersionCriteria                              crit,
                                    IEnumerable<Dictionary<string, AvailableModule>> available,
-                                   Dictionary<string, HashSet<AvailableModule>>     providers,
-                                   Dictionary<string, InstalledModule>              installed,
+                                   IDictionary<string, HashSet<AvailableModule>>    providers,
+                                   IDictionary<string, InstalledModule>             installed,
                                    ICollection<string>                              dlls,
                                    IDictionary<string, ModuleVersion>               dlc)
         {
@@ -103,9 +103,9 @@ public ICollection<CkanModule> LatestIncompatible
             }
         }
 
-        private readonly Dictionary<string, InstalledModule> installed;
-        private readonly ICollection<string>                 dlls;
-        private readonly IDictionary<string, ModuleVersion>  dlc;
+        private readonly IDictionary<string, InstalledModule> installed;
+        private readonly ICollection<string>                  dlls;
+        private readonly IDictionary<string, ModuleVersion>   dlc;
 
         private List<CkanModule>? latestCompatible;
         private List<CkanModule>? latestIncompatible;
@@ -119,8 +119,8 @@ public ICollection<CkanModule> LatestIncompatible
         /// Mapping from identifiers to compatible mods providing those identifiers
         /// </returns>
         private static Dictionary<string, HashSet<AvailableModule>> CompatibleProviders(
-            GameVersionCriteria                          crit,
-            Dictionary<string, HashSet<AvailableModule>> providers)
+            GameVersionCriteria                           crit,
+            IDictionary<string, HashSet<AvailableModule>> providers)
             => providers
                 .AsParallel()
                 .Select(kvp => new KeyValuePair<string, HashSet<AvailableModule>>(
diff --git a/Core/Registry/Registry.cs b/Core/Registry/Registry.cs
index 3086a4ca3..bec1acdcf 100644
--- a/Core/Registry/Registry.cs
+++ b/Core/Registry/Registry.cs
@@ -42,11 +42,11 @@ public class Registry : IEnlistmentNotification, IRegistryQuerier
 
         [JsonProperty]
         [JsonConverter(typeof(JsonParallelDictionaryConverter<InstalledModule>))]
-        private readonly Dictionary<string, InstalledModule> installed_modules;
+        private readonly IDictionary<string, InstalledModule> installed_modules;
 
         // filename (case insensitive on Windows) => module
         [JsonProperty]
-        private Dictionary<string, string> installed_files;
+        private IDictionary<string, string> installed_files;
 
         /// <summary>
         /// Returns all the activated registries.
@@ -55,9 +55,8 @@ public class Registry : IEnlistmentNotification, IRegistryQuerier
         /// </summary>
         [JsonIgnore]
         public ReadOnlyDictionary<string, Repository> Repositories
-            => repositories is not null
-                ? new ReadOnlyDictionary<string, Repository>(repositories)
-                : new ReadOnlyDictionary<string, Repository>(new Dictionary<string, Repository>());
+            => new ReadOnlyDictionary<string, Repository>(repositories
+                                                          ?? new SortedDictionary<string, Repository>());
 
         /// <summary>
         /// Wrapper around assignment to this.repositories that invalidates
@@ -342,9 +341,9 @@ private Registry(RepositoryDataManager? repoData)
         }
 
         public Registry(RepositoryDataManager?               repoData,
-                        Dictionary<string, InstalledModule>  installed_modules,
+                        IDictionary<string, InstalledModule> installed_modules,
                         Dictionary<string, string>           installed_dlls,
-                        Dictionary<string, string>           installed_files,
+                        IDictionary<string, string>          installed_files,
                         SortedDictionary<string, Repository> repositories)
             : this(repoData)
         {
@@ -857,8 +856,9 @@ public void RegisterModule(CkanModule   mod,
                 installed_files[file] = mod.identifier;
             }
 
-            // Make sure mod-owned files aren't in the manually installed DLL dict
-            installed_dlls.RemoveWhere(kvp => relativeFiles.Contains(kvp.Value));
+            // Make sure this mod and its files aren't in the manually installed DLL dict
+            installed_dlls.RemoveWhere(kvp => kvp.Key == mod.identifier
+                                              || relativeFiles.Contains(kvp.Value));
 
             // Finally register our module proper
             installed_modules.Add(mod.identifier,
@@ -916,9 +916,12 @@ public void DeregisterModule(GameInstance inst, string identifier)
         /// Does nothing if we already have this data.
         /// </summary>
         /// <param name="dlls">Mapping from identifier to relative path</param>
-        public bool SetDlls(Dictionary<string, string> dlls)
+        public bool SetDlls(IDictionary<string, string> dlls)
         {
-            var unregistered = dlls.Where(kvp => !installed_files.ContainsKey(kvp.Value))
+            var instIdents = InstalledModules.Select(im => im.identifier)
+                                             .ToHashSet();
+            var unregistered = dlls.Where(kvp => !instIdents.Contains(kvp.Key)
+                                                 && !installed_files.ContainsKey(kvp.Value))
                                    .ToDictionary();
             if (!unregistered.DictionaryEquals(installed_dlls))
             {
@@ -930,7 +933,7 @@ public bool SetDlls(Dictionary<string, string> dlls)
             return false;
         }
 
-        public bool SetDlcs(Dictionary<string, ModuleVersion> dlcs)
+        public bool SetDlcs(IDictionary<string, ModuleVersion> dlcs)
         {
             var installed = InstalledDlc;
             if (!dlcs.DictionaryEquals(installed))