When the filename ends with the ? character no tags are displayed (I have only flac and dsf files). Deleting the ? and the tags are properly displayed.
Example filename is 01-perche?.flac no tags are displayed. Changing filename to 01-perche.flac makes mp3tag display the tags
Basically, this applies:
The following are reserved characters:
< (less than)
> (greater than)
: (colon)
" (double quote)
/ (forward slash)
\ (backslash)
| (vertical bar or pipe)
? (question mark)
* (asterisk)
Integer value zero, sometimes referred to as the ASCII NUL character.
Characters whose integer representations are in the range from 1 through 31, except for alternate data streams where these characters are allowed. For more information about file streams, see File Streams.
Any other character that the target file system does not allow.
That is why I referred to the Windows conventions.
As MP3tag on a Mac runs in a windows emulation it still means that filenames have to comply with windows rules.