this image shows binary code of a file edited by mp3tag v2.79.
Address 0x2F is end of TALB UTF-8 data however the data not terminated with $00,
continuing next TPE1 UTF-8 data without terminating.
The reported issue is now fixed with the current Development Build (Mp3tag v2.80a). It actually applied not only to UTF-8, but also to ISO-8859-1 and UTF-16.
As with all those low-level changes, it would be great if you (and possibly others) can analyze the new implementation and confirm the fix.