I have the same "malfunction". I can make seemingly perfect practice swings then get over the ball and suffer from what I will call "impact blackout". I have heard the term downswing blackout, but I think it is the concious and/or subconcious distraction of impact that is the source of the maledy.
My guess is that this is a fairly common thing that only gets worked out with practice and confidence in ones swing (or maybe we start swinging blindfolded?.....lol)