Created Unassigned: AvalonDock problems with adorners [22418]

I'm using Adorners to bring some messages in my application.
The Aplication layout is made with Avalonedoc (wpf toolkit 2.9 comunity edition. is reporucable with 2.8)

When I'm trying to add Adorner to Avalonedoc Unpinned Pane an NullReferenceException acures. If I add an adorner to pinned panel the the adorner gets lost after you Hide/show the panel.
In atchments you can find litle project, which represnts the beheviour