Tag panel does'nt keep file tags (created or changed) if file not saved.
Suppose you have 2 files in main panel.
Edit tags for file1 then select file2 the go back selecting file1: all tags for file 1 are lost.
Maybe you do noy consider that as a bug but it is a very disturbing behavior.
Hello there. I've moved the topic from the Bug Reports category, as I think it's not a bug in Mp3tag.
Instead, you can enable Save tags when using arrow keys/single mouse click at Options > Tags to automatically save any changes to the selected files when navigating to a different file.
You habe to activate this feature in
Tools -> Options ->Tags -> Save Tags ....