Originally Posted by
mville
In MP3Tag, right-click on a flac and select Extended Tags... In the Extended Tags window you should see all tags listed.
Please can you confirm that DISCNUMBER, DISCTOTAL, TRACKNUMBER and TRACKTOTAL are not in the list?
These 4 tags may be named differently, depending on any mapping you have used in dBpoweramp Configuration and/or MP3Tag. For vorbis comments I have TRACKNUMBER mapped to TRACK in MP3Tag and I use the default mappings for FLAC ID Tagging in dBpoweramp Configuration.