Bail closes during cast?

I recently got back into fishing and was having problems with my
spinning reel such that the bail closes by itself mid cast. It was a
cheap reel, so I got a new shimano reel ($40 range), and sure enough,
it snaps shut during a cast now and then. Is this a bad technique?
Does it have something to do with the position of the crank during the
cast, whereas the snap action makes the crank turn and the bail
closes? Is there anything I could adjust mechanically to help keep
the bail open during a cast?

I just got a baitcasting reel, but I want to be able to use both
reliably.

any hints?

--edfardos