After window thumbnail from taskbar was shown, the frame of the thumbnail is seen until any other window gets activated.
Steps to Reproduce:
1. Activate a thumbnail via taskbar
2. Deactivate it, but do not activate anoher window
Created attachment 76033 [details]
image of the artifact
The artifact is between two black frames
Assuming those are tooltips as well?
*** This bug has been marked as a duplicate of bug 311502 ***