Bug - Drop on Pane Dock breaks Layout

[sskk-johannes]

When moving an auto hidden pane onto one of the inner pane docks, the layout breaks irreversibly.
This seems to only occur when dragging between vertical and horizontal orientation.

How to reproduce:

1. Open TestApp
2. Drag pane onto left inner dock
3. Set pane to auto hide
4. Click pane and drag to top inner dock
   These steps may have to be repeated a couple of times to take effect.

We tried to debug the issue, but so far were unable to find the source.
We have looked into DocumentPaneDropAsAnchorableTarget.Drop and LayoutAnchorable.ToggleAutoHide.
Any other advice on additional relevant code that handles the layout would be much appriciated.

autohide_bug.mp4