I'm using Mp3tag for quite a while but just discovered that Actions are exactly what I need I'm running Mp3tag in Wine as there is no such good and usable tool natively on Linux. I created some Actions for my usual workflows and discovered a bug (I think).
I am using the "Format value" action for _FILENAME and this format string: "%artist%%album%$num(%track%,2) - %title%.%_extension%"
"Z:\home\user\Music\ToDo\Artist with Questionmark_\AlbumX\01 - Title.mp3"
cannot be renamed to
"Z:\home\user\Music\Artist with Questionmark\AlbumX\01 - Title.mp3"
Path not found
The artist is "Artist with Questionmark?" which is of course not a valid path for Windows software. The "Tag -> Filename" feature which I used to use did never have a problem with this, though (even under Wine). It just removes the invalid characters from the path. So my guess is that at this point the paths aren't sanitized correctly/completely.