Found a bug and reported it to Tivo Support... If you are watching a recorded show, and while it's playing you go to the guide and record something, upon setting up the recording the show you were watching goes back to the beginning...
Surprisingly the rep said they hadn't gotten a lot of calls about this, so please call and let them know so we can get this fixed asap.
Try it, you'll see what I'm talking about... It's very annoying, especially if you're watching a sporting event!