In the second case where the ID3 v.1 tag "won" over the v.2 it was 2.4.

In the second case I may be wrong upon closer inspection. It seems my flac files use a different kind of tags, set/manipulated by Mozilla Songbird.

OK. Closer inspection and some googling. It is <edit>flac metada</edit> that the media player does not recognize. My bad. Sorry.

(However, it should, IMHO, but since it does not support Vorbis formats out of the box, this might not be high on Nokia's radar...)