I just ran into this, a field will accept a "set" object for the choices argument, however since set objects are unordered, it's possible that a new migration will be created every single time makemigrations is run.
debugging this was a matter of noticing that the developer used curly braces instead of parentheses or brackets, it could have been very sticky. Wondering if this should raise a TypeError -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/8b1364f4-8c06-49b3-87c6-e9073ddb1e3en%40googlegroups.com.

