DVR selectively recording episodes -- though set to "record both"

My son is a Spongebob fanatic. If he doesn't have an episode of Spongebob to watch while he gets ready for school in the morning, the world may actually stop turning. We have it set to record on both Nickelodeon East and West. Both episodes (not first run only). And both channels are set to hold 10 episodes. There was a time when we could reliably turn on the DVR and have a nice big list of Spongebob ready for viewing. However, in the past month or so the DVR has all but stopped recording them. There will occasionally be an episode listed, but we're getting maybe four episodes recording a week now. And if you know your Spongebob -- that show is on ALL the time! We will go to the "To Do" list and see that tomorrow, its supposed to be recording Spongebob after Spongebob. But then tomorrow comes and they've vanished from the list. They are on -- its just not recording them.

Anybody have any suggestions as to what might be going on? The obvious: No, there is not a conflict. We don't DVR many shows. Mainly prime-time series. And there is nothing recording (let alone two things!) against Spongebob. Also, we delete episodes once we've watched them, so its not an issue of repeated episodes not recording because they're already sitting in our list. Right now, there is NO Spongebob on our DVR. Help!