After a long time I decided to upgrade from version 2.57 to 2.70 (yes I know, it is an 'oldy' but it did the job I needed it to do).
I opened a folder with mp3's which I updated with 2.57 some month's ago. After loading only the also embedded ID3v1 tags were recognized. The v2 showed a !BAD ID2v3 indication. Switching back to 2.57 the tags were read without error.
Tried to write some tags with other programs like Foobar2000. Opening them in 2.70 always shows the error where 2.57 read them without error.
After some extended testing it seems the error shows when cover art is available. Tried various settings for ID3v2.3 and 2.4 with different character encodings
Since I do not have other (intermediate) releases I can not check which version starts with the error.
No bug. Running newer version of mp3tag on wine needs version 1.7 of wine.