Like you said Garry, changing to Avalonia 12 will cause bugs.
I experience multiple problems in Objo Windows.
Dragging a control: once placed on a window I can't select it anymore. It is still there but doesn't respond to the mouse.
Switching from designer to code and back: immediate crash. Tried this several times.
Edit: I noticed when this happens when a TabPanel is placed in the window. Dropping buttons will cause weird behaviour and switching from designer to code results in a crash.
Hope you can fix that?
Alexander