ID3 v2.4? I don't know anything about that, is that a type of tag format? Concerning FLACs, to be honest while having these issues, I haven't been keeping track of which files have and have not been going wrong. Some files I have are MP3, some FLAC. I would hazard a guess and say actually, I think the issues I've been having have been with my MP3 files.
Concerning WMP, I do have that and have been using it longer than anything else. I don't use it to edit anything whatsoever though, I just use it to open individual podcasts, and to sync podcasts to a seperate MP3 player I only use for podcasts. But WMP is often running in the background when I'm doing other stuff. I remember ages ago, being bothered that it always seems to be 'updating' while it's running. I can't remember the exact wording, but it would be updating something from online. I actually remember a few years ago worrying about it messing up tags in my MP3 files, but it didn't appear to do anything, so I left it.
But maybe it is doing something now. I don't know why it would suddenly be an issue now, after all this time. Like somethings triggered it, weird. But actually about an hour ago, before I read your post, I did think of that. So I switched off the option under 'library' which is called something like 'update library data', just incase. I have never used it to edit my songs, though. I mean I guess it automatically looks in Windows default music folder, but the folder containing my songs is in a diff folder on an externall HDD. I never set WMP to look in there.
On a side note, I have stopped using MP3Tag 2.64 to try to fix the files. Even though I started using it in the first place to fix a problem, I think to add to the confusion, it's caused extra issues. So having several issues at almost the same time has confused me, making me think they're one in the same. MP3Tag may have been what deleted most of the fields on a lot of my tags, through some weird bug. While something else (maybe MB) is what's causing the other issues like spliting the albums up and renaming them. Or maybe it's the other way around. All I know is that my original issues weren't as bad. Just some covers dissapearing and albums splitting themselves into 2 and 3 parts. But when I tried to fix that issue a little while later, bigger problems like many files just losing their tag fields completely occured.
So what I've started doing is edit the tags by using MB completely. It didn't seem to work at first, but if I select the multiples of a split album by control + click, then edit, then rename the album artist to the same thing (even though they were the friggin same originally), then rescan the folder with MB. It then seems to re-connect the albums back together. I just hope it sticks this time, and doesn't just start to randomly freak out again. It will mean taking longer to edit tags, but I'll have to get used to it. I'm more used to tagging with MP3tag and Tag&Rename, they seem faster for tagging loads of files at the same time. But I'm guessing MB will be just as fast if I get used to it.
I've changed the title of this thread, as I'm now thinking I was being a little harsh.