Incorrect Master IDs?

Hi there!

Sometimes when I ask for a GSmaster’s ID via python, I receive a value such as ‘master01’, rather than a long alphanumerical string, as is the case with a ‘new’ file/master in a Glyphs file.

Then when I ask for the master at ‘master01’, Glyphs throws an error claiming that master is not there.

Is this something that changed about the API/Glyphs? Were older files (prior to ~ 2 years ago) using master IDs in the ‘master__’ format?