Created attachment 298209 [details]
After starting VLC

To reproduce:
1.) Open VLC (or SMplayer or any app in fullscreen mode).
2.) Start watching a movie and go to fullscreen mode.
3.) Alt+tab to another open application
4.) Alt+tab back to VLC
After getting back to VLC you will see a white stripe on the top of the screen as on the attached screenshot.

I have tried this with other applications like Firefox and the default video player (Totem).
They produce a slightly different symptoms as they also have a white stripe on the left of the screen besides the top, but I would bet it is the same bug.
In Totem the white stripes are also blinking a bit.

I'm attaching 2 screenshots.
1.) After starting VLC where everything is okay.
2.) After alt+tab ing with VLC where the white stripe is already displayed.

I'm using gnome-session-flashback (gnome-panel) with metacity.
I'm not sure which of them is responsible for this or if one of them even is but they seem to be the best candidates.

I have also installed Xfce on the same machine and players started in Xfce do not produce similar problems.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: metacity 1:2.34.13-0ubuntu4
ProcVersionSignature: Ubuntu 3.13.0-46.75-generic 3.13.11-ckt15
Uname: Linux 3.13.0-46-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.7
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Mar  1 14:54:32 2015
SourcePackage: metacity
UpgradeStatus: No upgrade log present (probably fresh install)