Sometimes, after pasting a cover jpg or removing a cover, the details of the track are cleared when I save the track. This affects only the display, not the track itself.
The details can be brought back by doing a refresh, but I have accidentally written the blank values back to the track, and had to re-create them by hand...
I'm using version 2.69 but I've had this problem for many releases. My system is Win7 x64, but I think I had the problem even back on XP. Yes, I've had this problem for years.
I didn't want to try the development version as this bug has been around for ages, so it's unlikely to have been fixed recently. And there's the pitfall of losing the track settings to worry about...
Since this is a rather upsetting bug, I presume that it affects only me (or only people who don't complain?). I suspect you won't be able to reproduce it.
As a programmer, I know how frustrating this can be, so I'm perfectly happy to run a modified version to trap the problem. If there's any tracing that I can turn on, please show me how.
But MP3Tag doesn't crash, so it might be hard to spot the problem in a trace. The modified version could perhaps crash deliberately when most of the track fields go blank (I'll record the exact columns affected on the next error).