I had 2 failed recordings yesterday evening. I was using the live pause on Top Gear BBC HD, while there were 2 timer recordings set for different channels at the same time.

There is a broken icon symbol next to the failed recordings, and if I select them its an Uknown error. The only thing that works is to delete the item.

Is there some combination of features that leads to broken recordings?

The only thing I know that guarantees that you will get a broken recording (apart form a conflict which often gives an unnecessarily pessimistic message even if you've only missed a couple of seconds) is where the box stops (Power failure, turned fully off or spontaneous reboot) after at least 30 seconds of recording have been made.

The other 'unknown reason' failures seem to be just that: 'unknown'.

It's annoying because the software must have come to set that flag by some path and knowing that path would at least be a clue.

The two possibilities that spring to mind (other than the ones just mentioned) are:

Programme was in guide but no start flag received.
Programme was started but ended before 30 seconds had recorded.