Yesterday morning my DVR had 20% remaining storage capacity.  I had only a couple programs scheduled to be recorded.  There were no (!) indicators that anything was about to be deleted.  I had been having some pixelization and freeze problems that day so i reset both my gateway and DVR.  As usual that cleared up the problem.  Later in the day I noticed that for no apparent reason over 25 recordings (all in one show category) were erased.  Capacity after the deletions was 50%.