Looks like an issue about taking snapshot of fullscreen app.
Android's Task Manager just cut the screenshot to match a square, so this may be a UX decision.
Created attachment 676949 [details] Cardview of the video app Looks like so. Another fullscreen app has the same issue. Note that this effect also makes the opening transition first display the cropped image then the correctly rendered app; it makes a "jump" feeling.
Cant reproduce in 2.1 or master