First I have to thank for the new firmware features (and hopefully the full_volume_at_songchange bug fix)!
My problem is(was), that the fuze froze at the database rebuild after installing the new firmware. I removed all music and copied it back on the fuze album-by-album and found the hang is caused by OGG files that didn’t cause problems with the .22 firmware.
The problematic OGG files have been tagged using MusicBrainz Picard, ver. 0.11, under linux. Removing all metadata from the OGG files solves the DB update problem.
Later I found the vorbissort script mentioned here
that also cures the database update problem and allows to keep all tags. (BTW: the vorbissort was written to solve problems regarding coverart in the tags, which I don’t use.)
It seems that MusicBrainz Picard writes the tags in a way that confuses the fuze, even though the Picard tagged OGGs play flawlessly in several software players on my PC.