I've just released Mp3tag v3.33.1 which includes bug fixes and other improvements that have been reported since the last release. If you're curious, the changelog has the complete list.
Most notably, it reverts back to the previous behaviour where it doesn't try to preserve umodified ID3v2 frames and MP4 atoms. When saving, Mp3tag now writes tags according to its documented internal mappings by default.
If someone prefers minimal changes applied to the tag, I've added the configuration options Reuse unmodified ID3v2 frames and Reuse unmodified MP4 atoms at Options → Tags → Advanced.
If those options are enabled, existing user-defined fields for which a mapping exists are not remapped to the target representation unless the field value changes. As a result, mapped fields are only rewritten when their corresponding field contents are modified.