i've got the Problem that Mp3 Tag shows the Popularimeter Tag of a mp3 or ogg File as RatingMM when the Song is ratet with 1 or 5 Stars. All other Ratings between 1 and 5 are correctly shown as Popularimeter.
When i Open the Files in an Hex Editor or Text editor there is only the Poularimeter Tag.
You are right, there is only one POPM field.
But depending on the format in the field, MP3tag shows it as
POPULARIMETER
Rating MM
Rating WMP
Rating Winamp
You see POPULARIMETER if the numbers are higher than 5 and there is at least one | in the field.
You see the others if you find a - for half a star or a chain of asterisks or a number not higher than 5.
WMP, for instance, translates the high numbers from Popularimeter to its star notation.
So I would suspect that one or the other POPULARIMETER field had higher values than 5 in it which then got translated to one of the other displays.