diff --git a/source/Components/AvalonDock/DockingManager.cs b/source/Components/AvalonDock/DockingManager.cs
index a6a396d5..68658374 100644
--- a/source/Components/AvalonDock/DockingManager.cs
+++ b/source/Components/AvalonDock/DockingManager.cs
@@ -1138,7 +1138,7 @@ public double GridSplitterHeight
 				new FrameworkPropertyMetadata((Style)null));
 
 		/// <summary>
-		/// Gets or sets the GridSplitterVerticalStyle property.  This dependency property 
+		/// Gets or sets the GridSplitterVerticalStyle property.  This dependency property
 		/// indicates the style to apply to the LayoutGridResizerControl when displayed vertically.
 		/// </summary>
 		public Style GridSplitterVerticalStyle
@@ -1164,7 +1164,7 @@ public Style GridSplitterVerticalStyle
 				new FrameworkPropertyMetadata((Style)null));
 
 		/// <summary>
-		/// Gets or sets the GridSplitterHorizontalStyle property.  This dependency property 
+		/// Gets or sets the GridSplitterHorizontalStyle property.  This dependency property
 		/// indicates the style to apply to the LayoutGridResizerControl when displayed horizontally.
 		/// </summary>
 		public Style GridSplitterHorizontalStyle
@@ -2125,9 +2125,8 @@ private void DockingManager_Loaded(object sender, RoutedEventArgs e)
 			}
 			_fwHiddenList.Clear();
 
-			// load floating windows not already loaded! (issue #59 & #254)
-			var items = new List<LayoutFloatingWindow>(Layout.FloatingWindows.Where(fw => !_fwList.Any(fwc => fwc.Model == fw)));
-			foreach (var fw in items)
+			// load floating windows not already loaded! (issue #59 & #254 & #426)
+			foreach (var fw in Layout.FloatingWindows.Where(fw => !_fwList.Any(fwc => fwc.Model == fw)))
 				CreateUIElementForModel(fw);
 
 			//create the overlaywindow if it's possible
@@ -2292,7 +2291,7 @@ private void DocumentsSourceElementsChanged(object sender, NotifyCollectionChang
 					foreach (var documentToRemove in documentsToRemove)
 					{
 						documentToRemove.Content = null;
-						documentToRemove.Parent.RemoveChild(documentToRemove);
+						documentToRemove.Parent?.RemoveChild(documentToRemove);
 						RemoveViewFromLogicalChild(documentToRemove);
 					}
 				}
@@ -2354,7 +2353,7 @@ private void DocumentsSourceElementsChanged(object sender, NotifyCollectionChang
 				var documentsToRemove = GetItemsToRemoveAfterReset<LayoutDocument>(DocumentsSource);
 				foreach (var documentToRemove in documentsToRemove)
 				{
-					(documentToRemove.Parent as ILayoutContainer).RemoveChild(
+					(documentToRemove.Parent as ILayoutContainer)?.RemoveChild(
 						documentToRemove);
 					RemoveViewFromLogicalChild(documentToRemove);
 				}