In the video you can see that:
-
Attempt 1 and 2: Docking the toolbox over the properties panel directly (even while the mouse is moved) doesn’t generate errors.Never mind, it just took a few more tries. See the second video. - Attempt 3 and 4: Docking the toolbox above the properties panel, and then over the properties panel (without moving the mouse) doesn’t generate errors.
- Final attempt: Docking the toolbox above the properties panel, and then over the properties panel, and then moving the mouse around generates errors.
https://giant.gfycat.com/TimelyTartAnemone.webm
EDIT: Second video. It looks like you don’t need to dock the toolbox panel above the properties panel first to reproduce the bug after all.
https://giant.gfycat.com/BossyWhiteArizonaalligatorlizard.webm