When renaming using 'Action - Case conversion' menu on filename and title of mp3 files, for certain filenames a dialog occurs when trying to rename the filename. The dialog is presented for the user to verify the file name, but pressing OK in the dialog will only bring the dialog back with the same file name suggestion (infinite loop). Clicking Cancel in the dialog will cause the filename to remain unchanged.
It seems mp3tag is unable to rename a file when the first character of a word in the filename is to be "upper cased" and the first character in the word is either æ, ø or å. It is not a problem when changing case on the title, only on the filename.
As long as the æ, ø or å is positioned inside a word (so that no case change is to be performed on it) it works great.