When I copy a set of tags from one file and paste them to selected mutiple files, I get the message that the tags are being saved, however, the tags will only be saved to one of the selected files. The message box will say "saved tag in five of five files, " but ONE file is actually saved with the new tags!
check whether your file has also APE tags (select one of the tag-resistent files and press Alt-T: the heading of the then opened dialog box shows the tags stored in that file.)
If something like APE appears then delete all APE tags from the file.
Yes, I can confirm this behaviour in Mp3tag v2.45b too.
I've mentioned this case anywhere here in the forum, didn't I?
This behaviour is rather surprising.
It would be very helpful if "cut/copy one - paste multiple" could work.