Looks like the rough size of the bounding box my cursor was stuck in (maybe a bit smaller) when alt-tabbing out sometimes. It was random outside fullscreen osu!, and had 100% chance of happening in editor. Though, I didn't get any graphical anomalies you got. Also haven't found a way to reproduce since last time I restarted osu!.
agubelu wrote:It happens sometimes when I alt+tab away from osu and then come back to it. I haven't found a reliable way to reproduce it, it seems pretty random, but it always happens that way and is fixed by just moving the mouse.