I just found a minor bug. It isn't really serious as it doesn't cause the program not to work anymore, but I think this is also something the developers could fix quite quickly:
I just created a plane, and draw a freehand mask. Then, with the selection tool selected, I accidentally moved it to the right, so I pressed the undo button. It took the mask and set it where it was before, but the quad that indicates the bounding box of the mask remains in the position where it was before I undid it, as you can see in the attached picture. It's not that much of a problem, because simply deselecting the mask then selecting it again solves it, but it would be nice if you could fix that.