In at least some of the recordings I've made from the Finnish YLE- channels there is a small gap at the start of the actual program and VDR has chosen to record the rest of the program in a new file.
I'm guessing that the problem has something to do with subtitles and/or audio tracks, but I'm certainly no expert.
http://www.linuxtv.org/pipermail/vdr/2005-March/000873.html
When pids of a recorded channel are changed, vdr stops recording and (a few seconds) later starts it again with the new pids.
A long time ago I tried to do a quick hack to fix this. I tried to add the new pids to the running recording instead of stopping. I didn't care about removing the old pids, because with Yle channels the removed pids are not given to some other channels, but just not sent at all.
It turned out that adding the pids wasn't that easy. It seemed quite difficult to dig the necessary information out of vdr immediately. I have no idea if that has changed in recent years.
There might be a workaround for this problem: http://www.digita.fi/files/459/PID-arvot_A.pdf
Put all pids from that pdf to channels.conf and change vdr settings to not update pids.