Purchased movies won't play in Quicktime

I have the most recent Quicktime software for PC, and as of late, my movies purchased from the iTunes Store won't play properly. Some of them play just fine, but I recently bought Hellboy II and The Hobbit, and while they play in the iTunes Player, if I try to open them in Quicktime, I get a grey screen with no audio. The Hobbit one even shows a green bar at the bottom of the grey screen.

I greatly prefer Quicktime for movies since the iTunes Player seems to "lag" and makes them choppy sometimes.