I have a similar issue with the NowTV Channels except I find my box has a failed recording for something that I didn't actually set to record. Normally it's the same two programs from Sky Documentaries so it's definitely something that are or aren't doing with the data
I think we are saying the same thing.
In summary the recording is starting ok and continuing through the whole programme.
If the recording is stopped manually by pressing Record then everything up to that point is saved and can be viewed normally.
If the recording is allowed to terminate due to the EPG end setting, something interferes with the recording causing a Failure flag.
This only happens on the sky arts channel. As far as I am aware.
I have reported this to BT TV development and it is a known problem they are working on.
Don't hold your breath as it can take some time for things to be fixed!
For info, I just tried recording a couple of Sky Arts programmes on my Free sat box. The recordings are perfect.
I just did a preset recording on my (rather primitive) hard disk recording system on my TV and that recording is O.K. too. It does seem to be a problem with the BT TV software which they are working on.
First Freesat recording was manual start, auto end when programme finished, 2nd was set on the EPG. Both recorded fine.