Hey @piffy. Unfortunately this is an incompatibility with JS ‘Native class syntax’, EmberObjects’s reopen() functionality, and the @action decorator (which technically, creates a native JS ‘getter’).
I’m afraid I don’t have an immediate suggestion to get this particular override working, but we are working on a more robust solution for the future.
Depending on what you’re trying to do, maybe hooking into the badge model’s “save” function could work?