alright, now I got it, you're right this is a bug and that line should be change to be this:
String roleContext = this.config.getProperty(USER_ROLES_CTX, this.config.getProperty(ROLE_CTX));
so it should get the default value from the config properties instead of submitting the key there. I got confused when you passed the line with Context.ROLE_CTX.
I'll fix this as part of the issue already opened for it.
Thanks for detailed investigation