i took some time, to look again at the updatemedia process. (and now i won't look at the umlaut issue :-) )
But it seems not to handle updates very well.
how to reconstruct:
1. Take a nice tagged MP3 file. ( i just use id3v2 and ripped off all id3v1 tags, jsut to make sure)
2. Now i copy those files to the core
3. Webadmin/Files&Media/Media Files Sync choose the directory and resync manually. All looks fine until here
4. now i edit the tags through webadmin (change album title from "Absolutely Live -> Absolute"). The change is shown in webadmin, but not in the file itself (ok maybe the changes got not written back to file, don't know if lmce has this functionality))
5. take a windows mp3tag tool. Change the Album name to Absolute Li
6. Webadmin/Files&Media/Media Files Sync choose the directory and resync manually. Now i have two tags per file, one is "Absolute", second is "absolute Li". AND i have a composer field (which was unfilled) - which has the same Name "Absolute"