Index: Core/Gui/src/Core.Gui/Forms/MainWindow/MainWindow.xaml.cs
===================================================================
diff -u -r44a1619c9ffc6d60995d5ee42702271be0064727 -r3a3cef57bc0976a433e34bac53dc3790435d9d7d
--- Core/Gui/src/Core.Gui/Forms/MainWindow/MainWindow.xaml.cs	(.../MainWindow.xaml.cs)	(revision 44a1619c9ffc6d60995d5ee42702271be0064727)
+++ Core/Gui/src/Core.Gui/Forms/MainWindow/MainWindow.xaml.cs	(.../MainWindow.xaml.cs)	(revision 3a3cef57bc0976a433e34bac53dc3790435d9d7d)
@@ -326,6 +326,8 @@
                 stateToggleButton.IsChecked = false;
             }
 
+            gui.DocumentViewController.CloseAllViews();
+
             UpdateProjectExplorer();
         }
 
Index: Core/Gui/src/Core.Gui/Forms/ViewHost/DocumentViewController.cs
===================================================================
diff -u -r434415295de74c310ce6d3cdd0100c28838cf9ea -r3a3cef57bc0976a433e34bac53dc3790435d9d7d
--- Core/Gui/src/Core.Gui/Forms/ViewHost/DocumentViewController.cs	(.../DocumentViewController.cs)	(revision 434415295de74c310ce6d3cdd0100c28838cf9ea)
+++ Core/Gui/src/Core.Gui/Forms/ViewHost/DocumentViewController.cs	(.../DocumentViewController.cs)	(revision 3a3cef57bc0976a433e34bac53dc3790435d9d7d)
@@ -115,6 +115,14 @@
             return true;
         }
 
+        public void CloseAllViews()
+        {
+            foreach (IView view in viewHost.DocumentViews.ToArray())
+            {
+                viewHost.Remove(view);
+            }
+        }
+
         public void CloseAllViewsFor(object data)
         {
             if (data == null)
Index: Core/Gui/src/Core.Gui/Forms/ViewHost/IDocumentViewController.cs
===================================================================
diff -u -r434415295de74c310ce6d3cdd0100c28838cf9ea -r3a3cef57bc0976a433e34bac53dc3790435d9d7d
--- Core/Gui/src/Core.Gui/Forms/ViewHost/IDocumentViewController.cs	(.../IDocumentViewController.cs)	(revision 434415295de74c310ce6d3cdd0100c28838cf9ea)
+++ Core/Gui/src/Core.Gui/Forms/ViewHost/IDocumentViewController.cs	(.../IDocumentViewController.cs)	(revision 3a3cef57bc0976a433e34bac53dc3790435d9d7d)
@@ -50,6 +50,11 @@
         bool OpenViewForData(object data, bool alwaysShowDialog = false);
 
         /// <summary>
+        /// Closes all views.
+        /// </summary>
+        void CloseAllViews();
+        
+        /// <summary>
         /// Closes all views for <paramref name="data"/>.
         /// </summary>
         /// <param name="data">The data object to close all views for.</param>