I've been using Mp3tag for the past hour or so fixing a lot of files that WMP for some reason couldn't read (found out, for the most part, that it was because they were primarily ID3v2.4, and so opening them up and resaving the tags worked. However, I've also run into some mp3s with varieties of the same issue. There seems to often be a phantom tag that only shows up when I go to remove the tag (either through Remove Tag or Tag Cut), and is then able to be replaced with a Tag Copy. Even with some of the ones that don't have that phantom tag, I have to cut them so they turn blank and then paste the tags back on, and only after this do the tags display properly in WMP or Windows Explorer. As demonstrated in this gif:
Most of the phantom tags are ID3v2.4, which WMP and Explorer are incapable of reading or editing. It's like they are totally unable to handle it even being there, as editing anything in WMP still doesn't show up in Explorer. Zune Desktop is fully capable, however, as is Foobar2k and, I assume, Winamp.
Here's an MP3 that has this condition that you can use to check:
Just open File Explorer (I'm currently using Windows 7 Pro 64-bit) where that file is and see that none of the tag data is visible, open it in Mp3tag, see the data just fine and notice the tag says it's ID3v2.3, do a Tag Cut and see it change to 2.4, then paste and see it change back to 2.3 and the info is now visible in Explorer. Simply opening it up and saving the tag straight up doesn't help the situation. I am running the latest dev version of 2.60.