Created attachment 149834 [details]
Brief video showing observed effect
After snapping Firefox to any side, and then returning the window to windowed mode, a duplicate window is shown. See attached video. The same effect is seen in Lutris. I have not observed the same effect for any other application. Dissabling compositing removes this problem.
STEPS TO REPRODUCE
1. Drag Firefox to any side
2. Drag Firefox back to the middle
A duplicate window is seen on the right side.
*** This bug has been marked as a duplicate of bug 455617 ***