Track numbers from m4a files are not stored in the mediatomb database. The track_numer field in mt_cds_object is empty
Interestingly, all the information is present in the meta_data field of the database. There you see e.g. ...originalTrackNumber=6...
The problem is, that tracks of an album are not sorted correctly by track if the track_numer is missing but by name.
Regards
Wolfgang