I think this may be a format limitation rather than MP3Tag but I'm unsure. I have software that works with ID3V1 and ID3V2 but not APE tags. It uses Winamp to playback the music and in general works nicely with APE files. My problem is with compilation marking, it use a custom tag, I can create and manipulate this tag within ID3V2 MP3s fine but not APE files.
I assume ID3V1 cannot support custom tags but it seems MP3tag can only delete ID3 V2 tags from APE files and cannot add them. Should I be trying to add ID3V2 tags to the ape files? Is there any was of creating a custom tag with ID3V1?