I've got a few mp3 albums that, despite displaying all information in Windows Explorer (Win7 x64 here), will list the tag version as !BAD vx.x (where "x.x" is usually 2.3). When this happens, no other information is displayed in mp3tag. I've figured out that the way to solve the problem is to go ahead and save the tracks in mp3tag anyway, then enter the desired info in Windows Explorer, then double-check in mp3tag that this saved correctly (it typically does). Is there any quicker way, such that the information that is initially displayed in Windows Explorer could be salvaged?
You could experiment with the settings in Options > Mpeg to find out in which kind of tags the information is stored, then read in only this kind of tags but write only mp3 tags.