Trying dock a floating window inside a document pane leads to its disappearing of window's content.

[cuellius]

I use this xaml:

    <avalondock:DockingManager x:Name="DockManager" Grid.Row="2" Margin="0,0,0,0">
        <avalondock:LayoutRoot x:Name="MainLayoutRoot">
            <avalondock:LayoutPanel x:Name="LayoutPanelHost" Orientation="Vertical">
                <avalondock:LayoutDocumentPaneGroup x:Name="MainLayoutDocumentPaneGroup">
                    <avalondock:LayoutDocumentPane x:Name="InitialDocumentsPane">
                        <!-- here documents added in code -->
                    </avalondock:LayoutDocumentPane>
                </avalondock:LayoutDocumentPaneGroup>
            </avalondock:LayoutPanel>
        </avalondock:LayoutRoot>
    </avalondock:DockingManager>

In code I add documents (two or greater):

//DocumentViewer is my class, the class is derived from LayoutDocument
var dw = new DocumentViewer(); 
InitialDocumentsPane.Children.Add(dw);

I make floating the one document, then dock in inside this document, after this it do not dock, but disappears.

Reason: DocumentViewer is not fully class LayoutDocument, it is derived.

Fixing: class DocumentPaneDropTarget (file DocumentPaneDropTarget.cs), method protected override void Drop(LayoutDocumentFloatingWindow floatingWindow), switch (Type), case DropTargetType.DocumentPaneDockInside, replace loop

foreach (var anchorableToImport in layoutDocumentPaneGroup.Descendents().OfType<LayoutContent>()
 .Where(item => allowedDropTypes.Contains(item.GetType())).ToArray())

with

foreach (var anchorableToImport in layoutDocumentPaneGroup.Descendents().
 Where(d => d is LayoutDocument || d is LayoutAnchorable).OfType<LayoutContent>().ToList())

I am sorry, because I am very stupid and don't know how to create pull request.