Index: Core/Common/src/Core.Common.Gui/RingtoetsGui.cs
===================================================================
diff -u -r0d7895f07d2c1b15457ffdc8e8762780a5837030 -rd262d2ed2c6937c2bb555429ae46dc40780720cb
--- Core/Common/src/Core.Common.Gui/RingtoetsGui.cs	(.../RingtoetsGui.cs)	(revision 0d7895f07d2c1b15457ffdc8e8762780a5837030)
+++ Core/Common/src/Core.Common.Gui/RingtoetsGui.cs	(.../RingtoetsGui.cs)	(revision d262d2ed2c6937c2bb555429ae46dc40780720cb)
@@ -216,6 +216,7 @@
 
                 if (ToolWindowViews != null)
                 {
+                    toolWindowViews.CollectionChanged -= ToolWindowViewsOnCollectionChanged;
                     ToolWindowViews.Clear();
                 }
 
@@ -237,13 +238,16 @@
 
                 if (toolWindowViews != null)
                 {
-                    toolWindowViews.Clear();
                     toolWindowViews.Dispose();
                     toolWindowViews = null;
                 }
 
                 if (documentViews != null)
                 {
+                    documentViews.ActiveViewChanging -= ActiveViewChanging;
+                    documentViews.ActiveViewChanged -= OnActiveViewChanged;
+                    documentViews.CollectionChanged -= DocumentViewsCollectionChanged;
+
                     documentViews.Clear();
                     documentViews.Dispose();
                     documentViews = null;
Index: Core/Plugins/test/Core.Plugins.ProjectExplorer.Test/ProjectExplorerGuiPluginTest.cs
===================================================================
diff -u -r0c64d8a6c718c0aa67403a16c94dd0c10f862455 -rd262d2ed2c6937c2bb555429ae46dc40780720cb
--- Core/Plugins/test/Core.Plugins.ProjectExplorer.Test/ProjectExplorerGuiPluginTest.cs	(.../ProjectExplorerGuiPluginTest.cs)	(revision 0c64d8a6c718c0aa67403a16c94dd0c10f862455)
+++ Core/Plugins/test/Core.Plugins.ProjectExplorer.Test/ProjectExplorerGuiPluginTest.cs	(.../ProjectExplorerGuiPluginTest.cs)	(revision d262d2ed2c6937c2bb555429ae46dc40780720cb)
@@ -19,6 +19,7 @@
     public class ProjectExplorerGuiPluginTest
     {
         [Test]
+        [RequiresSTA]
         public void RegisteringTreeNodeAddsToTreeView()
         {
             // Setup
@@ -71,6 +72,7 @@
         }
 
         [Test]
+        [RequiresSTA]
         public void ReopeningProjectExplorerKeepsCustomNodePresenter()
         {
             // Setup
@@ -125,6 +127,7 @@
         }
 
         [Test]
+        [RequiresSTA]
         public void GetTreeNodeInfos_ReturnsSupportedTreeNodeInfos()
         {
             // setup
Index: Core/Plugins/test/Core.Plugins.ProjectExplorer.Test/TreeNodeInfos/ProjectTreeNodeInfoTest.cs
===================================================================
diff -u -r0d7895f07d2c1b15457ffdc8e8762780a5837030 -rd262d2ed2c6937c2bb555429ae46dc40780720cb
--- Core/Plugins/test/Core.Plugins.ProjectExplorer.Test/TreeNodeInfos/ProjectTreeNodeInfoTest.cs	(.../ProjectTreeNodeInfoTest.cs)	(revision 0d7895f07d2c1b15457ffdc8e8762780a5837030)
+++ Core/Plugins/test/Core.Plugins.ProjectExplorer.Test/TreeNodeInfos/ProjectTreeNodeInfoTest.cs	(.../ProjectTreeNodeInfoTest.cs)	(revision d262d2ed2c6937c2bb555429ae46dc40780720cb)
@@ -105,6 +105,7 @@
         }
 
         [Test]
+        [RequiresSTA]
         public void ContextMenuStrip_Always_CallsBuilder()
         {
             // Setup
@@ -139,6 +140,7 @@
         }
 
         [Test]
+        [RequiresSTA]
         public void GetContextMenu_Always_AddsAddItem()
         {
             // Setup