Comment 10 for bug 898870

One side effect of this bug (at least, I assume this bug is the cause) is that when using alt-tab on a viewport which has a window from an adjacent workspace intruding 2px into it, selecting the unwanted window causes that window to fully move onto the current viewport.

My hardware setup is a single monitor plugged into an X220 laptop, with the laptop screen disabled (but the monitor is higher resolution than the laptop screen). I'm not sure if this qualifies as "horizontal virtual desktop size" of two or more.