There is another type of glitch with rental downloads as well. As already mentioned, you can normally begin playback within a few seconds, all good so far. However a couple of times I've paused a movie a few minutes in, then when I hit play again to resume, it refuses to do it until the movie download finishes, and it won't restart from the beginning either. I suspect the OP was seeing a similar problem where it decides for whatever (incorrect) reason it doesn't have enough buffered to attempt playback, when it actually does. It nearly always works properly though. It's rare that I have any issues renting movies.