Yeah, don't do that, you probably also degrade the sound quality... If you've confirmed it is something odd with multiple tags try this.
- Select a group of mp3 files (You might want to start with a smart playlist so you don't mess with any other format)
- Right-click and use Convert ID3 Tags > None (may need to repeat this step if multiple tags)
- Then right-click and use Convert ID3 Tags > v2.3 (v2.4 support still patchy from various accounts)
Downside is that it will lose any embedded artwork, but it should preserve all other meta-data, both tag-based and stored within the library itself.
In fact, if you use my CreateFolderArt script before and after updating the tags it should archive any artwork as a local Folder.jpg image for each album and then reinsert that image on the subsequent run... Check it out on a single album first. If it doesn't work as expected let me know and I'll tweak the script to achieve this end.
tt2