They aren't downloaded to the iPad. Only in the cloud. I have all my older movies showing up that are only in the cloud (the older movies even have the cloud symbol in the bottom right corner of the movie artwork in my library), it just takes several days after purchasing to show up. If I do download them, they show up but disappear if I delete them.
I've tried logging out of iCloud, and also turning "show purchases" off then back on. Still nothing. It seemed to be whenever I would charge my iPad at night, the new movie would show up. but that's not the case, I charged last night and a couple movies I purchased over the weekend didn't show up.