Up front I'll admit I've tried to re-produce this behavior and couldn't, but the fact that a crash caused data loss is disturbing, so I though I'd better submit it anyway.
MP3tag had been open for quite a while on my desktop, and I'd just changed directories.
I executed a tag copy and a tag paste.
I noticed that the track number was wrong on the track I'd copied from. I clicked on the TRACK field to edit it. It didn't take, so I clicked a second time. (I believe this triggered a PLAY inadvertently.) I clicked a third time, got the track field selected for editing, and entered new data. I got a popup error, saying that the file could not be opened for writing. Realized Windows Media Player was playing the file. I accepted the error, alt-tabbed to Windows Media Player, closed it. Alt-tabbed back to MP3Tag. Attempted again to edit the field. The error about the file not being able to be opened for writing appeared again. I accepted it. Then an error appeared saying the database had become corrupt, and that I needed to restart the app. The error text said that the playability of my source files would not be affected and my DB would be rebuilt on opening.
But, on opening, I noticed one less file in the file count. Nothing in recycle bin. Searched all my drives. The file I had originally copied the tags from and then tried to edit is apparently completely wiped from my hard drive. I have backups, fortunately, but this is very disturbing.
OS is Windows XP, SP3. MP3Tag version is 2.44. I think that's all relevant info.