Thanks for the clear report, project, and video. I’ve confirmed that this is a bug.
Avalonia’s routed mouse event was reaching both the child control and its parent, causing Objo Studio to raise a separate event for each. This has now been fixed so mouse events fire only on the innermost Objo control under the pointer. Clicking the background of a ContainerControl will still correctly fire the container’s own event.
The fix covers MouseDown, MouseUp, MouseMove, MouseDrag, MouseWheel, MouseEnter, and MouseExit, and will be included in the next release.
Tracked here: https://feedback.objo.dev/bug/1359