I've now properly had a look into this & the position of the mouse when having the main window docked to the top of the screen makes it easier to replicate.
The problem was the temp fix I'd put in place isn't correctly dealing with the classic main window expanding down instead of the issue that led to need to fix with the window expanding upward when docked to other windows.
I've got a change for the next build but like I noted earlier, I've got to take over the complete main window handling to properly resolve this.
-dro
