A really major 'bug' is where the PVR allows you to set 3 recordings that conflict via series link, the result being that none end up being recorded.
An example is in tonight's schedule at 9:00pm, C4 have a two programme series, "1066: The Battle for Middle Earth", the first was shown last night. I didn't notice this morning that the schedule wasn't updated for tonight and that I had also scheduled recordings for "The Incredible Human Journey" and "CSI: Crime Scene Investigation". I only noticed that the PVR did not come out of standby to record 15 minutes before the scheduled transmission so I'm assuming this is the problem. I'm not too fussy about CSI, so I removed this from the schedule and re-scheduled 1066, put the PVR back into standby and noticed the PVR go to 'active' standby.
You can see there wasn't a programme conflict when the programmes were scheduled initially, as "1066: The Battle for Middle Earth" started on a different day. It only conflicted today. I accept with a series, that episodes mostly occur at weekly intervals and therefore can see why this wasn't highlighted when first scheduled. However, you would have thought that the recording schedule should be 'checked' for conflicts each day and then flagged so you could make a judgement. The only problem with this is if you happen to be away on holiday for any length of time then you are scuppered either way!
I suppose you could argue that 1066 wasn't a series in the accepted sense as it only occurred over two days, but you can see there is an anomaly here that is difficult for the programmers to program for.