Yes you seem to be right, when I tried on a smaller canvas (2000 x 1700 px) it doesn't appear but when I work on bigger canvases (7000 x 6000 px) they appear again.

I actually managed to take a screenshot when one appeared, (it wasn't easy)

Hey, I've been trying out the program a bit, it got some really nice features and a lot of potential. I would like to purchase this program but I need to know if this is an issue that can be resolved. For some reason when I use the program I get a glitch where square black boxes start flashing all o...