It shouldn't do that if you've watched the episode already (I seem to recall the cutoff is if you've watched more than 5 minutes).HTH said:
But if the TiVo is forced to delete an unwatched episode it deliberately doesn't count that under the 28 day duplicates rule. So any season pass or wishlist will not consider additional airing of that episode a duplicate and will try to record them. (If the SP or Wishlist is set to First Run Only, it will only attempt to record airing for up to 28 days from when the guide data claims it first aired (Original Air Date))