On wayland, if you alt-tab from one window to another on different desktops using the slide animation, a dark shadow appears around the tabbox. If before the slide animation is over you invoke the tabbox again, you see this very dark shadow which abruptly disappears after the animation finishes. I could take a video if the text description is unclear.
Of course this happens to any "notification", including notifications triggered by notify-send, and notifications triggered by changes in volume, display brightness, etc. Could someone move this to the appropriate category as it doesn't concern tabbox specifically? Thanks!
*** This bug has been marked as a duplicate of bug 458970 ***