There are several factors that can cause this.
If you are recording a show that immediately follows the one in question, it will be on the next show.
Kinda sucks, but networks run their shows over the time and DVRs don't know that.
Usually, if the show has nothing after it, DVR records for a little bit after show is scheduled to end.
But you can always go in to to scheduled recording and extend time past the scheduled time by a few minutes (there are several options of time).