Witch 4.3.8 is out, and it fixes an issue we introduced (sorry!) in 4.3.7.
The problem was that, for users who have Witch set not to activate the selected item when the modifier keys are released, there would be a half-second or so where the panel sat onscreen after a selection was made and activated. That delay is now gone.
Update from the About tab within Witch’s settings, or just download a fresh copy from our site.