Index: Core/Common/src/Core.Common.Base/ApplicationCore.cs
===================================================================
diff -u -rf8109189a1cf9b9905556f12faf82c1035c283a4 -rc621c8ee0e3f645a82baedf1654f4d58d1632348
--- Core/Common/src/Core.Common.Base/ApplicationCore.cs	(.../ApplicationCore.cs)	(revision f8109189a1cf9b9905556f12faf82c1035c283a4)
+++ Core/Common/src/Core.Common.Base/ApplicationCore.cs	(.../ApplicationCore.cs)	(revision c621c8ee0e3f645a82baedf1654f4d58d1632348)
@@ -21,7 +21,7 @@
             }
         }
 
-        public IEnumerable<ApplicationPlugin> Plugins
+        internal IEnumerable<ApplicationPlugin> Plugins
         {
             get
             {
@@ -51,7 +51,7 @@
             applicationPlugin.Deactivate();
         }
 
-        public void Dispose()
+        public virtual void Dispose()
         {
             foreach (var plugin in Plugins.ToList())
             {
Index: Core/Common/src/Core.Common.Base/ApplicationCoreExtensions.cs
===================================================================
diff -u -rf8109189a1cf9b9905556f12faf82c1035c283a4 -rc621c8ee0e3f645a82baedf1654f4d58d1632348
--- Core/Common/src/Core.Common.Base/ApplicationCoreExtensions.cs	(.../ApplicationCoreExtensions.cs)	(revision f8109189a1cf9b9905556f12faf82c1035c283a4)
+++ Core/Common/src/Core.Common.Base/ApplicationCoreExtensions.cs	(.../ApplicationCoreExtensions.cs)	(revision c621c8ee0e3f645a82baedf1654f4d58d1632348)
@@ -38,5 +38,12 @@
                                   .Where(e => e.SourceTypes().Any(type => type == sourceType || type.IsAssignableFrom(sourceType)) &&
                                               e.CanExportFor(itemToExport));
         }
+
+        public static IEnumerable<DataItemInfo> GetSupportedDataItemInfos(this ApplicationCore applicationCore, object parent)
+        {
+            return applicationCore.Plugins
+                                  .SelectMany(p => p.GetDataItemInfos())
+                                  .Where(dataItemInfo => dataItemInfo.AdditionalOwnerCheck == null || dataItemInfo.AdditionalOwnerCheck(parent));
+        }
     }
 }
\ No newline at end of file
Index: Core/Common/src/Core.Common.Gui/GuiCommandHandler.cs
===================================================================
diff -u -rf8109189a1cf9b9905556f12faf82c1035c283a4 -rc621c8ee0e3f645a82baedf1654f4d58d1632348
--- Core/Common/src/Core.Common.Gui/GuiCommandHandler.cs	(.../GuiCommandHandler.cs)	(revision f8109189a1cf9b9905556f12faf82c1035c283a4)
+++ Core/Common/src/Core.Common.Gui/GuiCommandHandler.cs	(.../GuiCommandHandler.cs)	(revision c621c8ee0e3f645a82baedf1654f4d58d1632348)
@@ -237,7 +237,7 @@
                 Log.Error(Resources.GuiCommandHandler_AddNewItem_There_needs_to_be_a_project_to_add_an_item);
             }
 
-            var selectDataDialog = CreateSelectionDialogWithItems(GetSupportedDataItemInfos(parent).ToList());
+            var selectDataDialog = CreateSelectionDialogWithItems(gui.ApplicationCore.GetSupportedDataItemInfos(parent).ToList());
 
             if (selectDataDialog.ShowDialog(gui.MainWindow as Form) == DialogResult.OK)
             {
@@ -373,16 +373,9 @@
             // add more if more cases are found (like a pure wpf case, for example)
         }
 
-        private IEnumerable<DataItemInfo> GetSupportedDataItemInfos(object parent)
-        {
-            return gui.ApplicationCore.Plugins
-                      .SelectMany(p => p.GetDataItemInfos())
-                      .Where(dataItemInfo => dataItemInfo.AdditionalOwnerCheck == null || dataItemInfo.AdditionalOwnerCheck(parent));
-        }
-
         private IEnumerable<DataItemInfo> GetSupportedDataItemInfosByValueTypes(object parent, IEnumerable<Type> valueTypes)
         {
-            return GetSupportedDataItemInfos(parent).Where(dii => valueTypes.Contains(dii.ValueType));
+            return gui.ApplicationCore.GetSupportedDataItemInfos(parent).Where(dii => valueTypes.Contains(dii.ValueType));
         }
 
         private SelectItemDialog CreateSelectionDialogWithItems(IList<DataItemInfo> dataItemInfos)
Index: Core/Common/test/Core.Common.Tests/Gui/RingtoetsGuiTests.cs
===================================================================
diff -u -rcaeb44054bb58aa8c480f86e7922a60ecf0f08ef -rc621c8ee0e3f645a82baedf1654f4d58d1632348
--- Core/Common/test/Core.Common.Tests/Gui/RingtoetsGuiTests.cs	(.../RingtoetsGuiTests.cs)	(revision caeb44054bb58aa8c480f86e7922a60ecf0f08ef)
+++ Core/Common/test/Core.Common.Tests/Gui/RingtoetsGuiTests.cs	(.../RingtoetsGuiTests.cs)	(revision c621c8ee0e3f645a82baedf1654f4d58d1632348)
@@ -1,7 +1,6 @@
 using Core.Common.Base;
 using Core.Common.Gui;
 using Core.Common.TestUtils;
-using Core.Common.Utils.Collections;
 using log4net.Core;
 using NUnit.Framework;
 using Rhino.Mocks;
@@ -44,25 +43,18 @@
         {
             // Setup
             var mocks = new MockRepository();
-            var applicationPlugin = mocks.Stub<ApplicationPlugin>();
+            var applicationCore = mocks.Stub<ApplicationCore>();
 
+            applicationCore.Expect(ac => ac.Dispose()).Repeat.Once();
+
             mocks.ReplayAll();
 
-            var applicationCore = new ApplicationCore();
-
-            applicationCore.AddPlugin(applicationPlugin);
-
             gui.ApplicationCore = applicationCore;
 
-            // Precondition
-            Assert.AreEqual(1, applicationCore.Plugins.Count());
-
             // Call
             gui.Dispose();
 
             // Assert
-            Assert.AreEqual(0, applicationCore.Plugins.Count());
-
             mocks.VerifyAll();
         }
 
Index: Core/Plugins/src/Core.Plugins.ProjectExplorer/ProjectTreeView.cs
===================================================================
diff -u -rd121feba5299c86d7ac04a366ee869b163e43ec7 -rc621c8ee0e3f645a82baedf1654f4d58d1632348
--- Core/Plugins/src/Core.Plugins.ProjectExplorer/ProjectTreeView.cs	(.../ProjectTreeView.cs)	(revision d121feba5299c86d7ac04a366ee869b163e43ec7)
+++ Core/Plugins/src/Core.Plugins.ProjectExplorer/ProjectTreeView.cs	(.../ProjectTreeView.cs)	(revision c621c8ee0e3f645a82baedf1654f4d58d1632348)
@@ -131,7 +131,7 @@
             {
                 buttonFolderAdd.Enabled = true;
 
-                buttonFolderAddNewItem.Enabled = applicationCore.Plugins.Any(p => p.GetDataItemInfos().Any());
+                buttonFolderAddNewItem.Enabled = applicationCore.GetSupportedDataItemInfos(nodeTag).Any();
 
                 buttonFolderDelete.Available = treeView.SelectedNodeCanDelete();
                 buttonFolderRename.Enabled = treeView.SelectedNodeCanRename();