Forgot to mention that this happens when switching workspace too.
Switching from non-Steam workspace to non-Steam workspace: No flicker
Switching from non-Steam workspace to Steam workspace: Flicker
Switching from Steam workspace to Steam workspace: Flicker
Switching from Steam workspace to non-Steam workspace: No flicker
Hello @ScoreUnder, this is an inherent tendency when resizing all X applications and not specific to Steam. Any X application that is not ready to render the new dimensions of the resized window on the same frame the resize occurred can show uninitialized memory.
Nothing extracted yet.
This is demonstrated in a previous video: http://youtu.be/tdypcnuRRkY
When the steam windows resize (particularly noticeable when the dialog is closed near the end of the video) the wallpaper sometimes flickers on-screen. Steam is the only program that causes this.
I have seen this happen on ATI Radeon HD 7770 and Nvidia GeForce GTX 660 Ti, both using proprietary drivers.