my instance is when switching to one window argv[0] not repeditively clicking trying to cause it (which did work by the way) so your idea of it not allowing while in the middle of activating another window goes out the window on that one, a windows already active, i click to focus another one, its selected but doesnt switch.. It wasn't that i was clicking around them blindly really fast, a tab lit up, i clicked on it, the window did not switch.
Glad to hear other people have this issue tho so I know its not just me. although i seem to have it happen more frequently than others.