I beat Couch Potato once with a Ruby Medal, then proceeded to get a Hero Medal on every other song immediately after selecting it in the menu
Very confused ._.
So sorry this bug occurred to you! I can remember this happened to me as well a few months back. Since then I have fixed many bugs and just like 5 minutes ago (literally), I published the long-awaited Hot Dog Hero Update 1.2, so I can not 100% confirm that the bug you mentioned is gone, however, I also could not reproduce it on my machine anymore, so I am hopeful. Should it occur again please tell me! Thank you for playing! :)