I use MP3TAG to manage my tags. I just notice a bug..
If I put "fantasy" in the PUBLISHER area of a MP4 file (with MP3TAG), I will not see it in Wacup. Then If I use Wacup to manage the data and I enter "FANTASY" in the PUBLISHER area, I see FANTASY in the Publisher column BUT if I look in MP3TAG, I can see that something is wrong cause I have : fantasy\\FANTASY
If I refresh metadata in Wacup, the FANTASY is erased (nothing in the column) but not realy erased cause I always saw it in MP3TAG.
All this only in this field ((I use composer field also and no problem with this one...)
Just for your information. have a nice evening.