The problem was that sometimes there were quite a lot of missing frames
(jumpy picture), and at the other times there were none. I debugged VDR and
finally pinpointed the problem in the remuxer. It appears that Finnish
broadcaster company is (sometimes) sending PES packets longer than VDR
remuxer can handle. The fix is quite simple and did remove the problem for
me and for couple of others who tried the fix in Helsinki area.
I will keep it there for few days only. As the bandwidth is somewhat
limited, please try this only if you are experiencing problems with missing
frames or 'jumpy' picture. And if you do try, please report your success
and/or problems.