If I have my 1000S tuned to (say) ch 101 and start to watch a previous recording, does the buffer continue to record 101?
So when I finish watching a 1 hour recording I can then catch up with the 1 hour of ch101 that I missed?

Wouldn't it be incredibly easy to test this out yourself?

I can't test this out myself.

But I would say the Buffer is cleared as soon as you start watching a recording or change the channel.
If you want to catch up on the TV you've missed while watching a recording it would be best to record it.

I tried this out for you earlier. The buffer is reset until the playback terminates. Then it starts building from scratch.

In any case the buffer seems to reset on a change of now/next epg content. Pressing record only records the current programme content from the point you watched live.

Unlike the Foxsat-hdr you can't grab the entire timeshift buffer file (0.ts) and extract the bit you want.