I've been playing around with this some time and haven't really been able to define exactly when it appears, but I've found one sequence where it works every time for me:
I have a workspace with at least 2 windows in the taskbar (minimized). Lets call this workspace2.
I'm on workspace1 and jump to workspace2 (with Ctrl+Alt+Right-arrow)
I open/focus one of the window1 with Alt+Tab.
I minimize the newly focused window1 again.
I make an Alt+Tab and holding <Alt> down to see which window I am selecting. I select the window I just minimized (window1) and release the Alt to open window1. But it is window2 which get focus and unminmize.
Hope it is enough explanation...
fixed with rev. 22407