I just got off the phone with the RMV. After being on hold for about 30 minutes (annoying, but not a huge deal) I explained my problem to the woman who came on the line: that I gave them a California C & M1 license (passenger cars and motorcycles) and received a Massachusetts D license (passenger cars only) in return. She said she'll pull my application, double-check that I did, indeed have a California motorcycle license and that my application was properly filled out to reflect that (both true) and then add the motorcycle endorsement to my license free of charge. Took about 5 minutes of actually talking to a person and hopefully things will be fixed soon. Sadly it will apparently take until Wednesday before her request for my application paperwork goes through, but whatever, I can deal with that.