Damage tracking messed up when external monitor is disconnected.
I have a Dell XPS 13 with a high-DPI 3200x1800 (runs at 2x) display and an external monitor with a low-DPI 2560x1400 display. Normally, my laptop is plugged into the external monitor with the lid closed. When I disconnect and open the lid, everything switches over correctly except that something gets messed up with damge tracking and my mouse drags a square of back-ground across my terminal windows.
I think I only ever observed this with gnome-terminal; firefox (XWayland) seems ok. Also, it does eventually go away and I think resizing the window makes it go away entirely.