Since upgrading from version 2.91 to 2.92, it seems the ITUNNORM normalisation and ITUNSMPB gapless tags are no longer listed in the 'Extended tags' window.
Also, the ITUNESMEDIATYPE is no longer shown correctly - instead of the text value (e.g. Audiobook), it displays a unicode control character (e.g. U+0002).
Looks like both issues are fixed with that version - many thanks!
One other thing though, I noticed when comparing an .m4a file before and after tag editing (to make sure tags were saved correctly), it had the chpl atom added on save despite the original file having no chapters. Is that intended?
Thanks for confirming the fix! I've found it critical enough to release a new version so the issues are now fixed with Mp3tag v2.93.
Regarding the chpl: I'm writing this now if Apple gapless data is found. The chpl atom is Nero's way to keep gapless data and it's my hope that compatibility is increased by this.