Hover over select widget, press and hold mouse button, move mouse to one of the other select options and release button.
You will notice that after releasing mouse button, the list will stay open. You'll need to click again to confirm.
This only happens when there is onmousedown/onmouseup event listener set up for document (see source).
First seen in build 8225, maybe introduced by this fix:
Probably affects only windows version (there seems to be no problem in Linux at least).