Replying to Tim Graham:
Did you mean to title the ticket "Model.save() doesn't validate CHOICES"?
Yes. Sorry for the incorrect title, I fixed that.
This is documented:
Note, however, that like Model.full_clean(), a model’s clean() method is not invoked when you call your model’s save() method.
OK, I think I did not pay enough attention to the point that saving and validation are two different steps, as documented in the model instance reference, and fields are generally validated during clean() except for explicitly documented cases like unique (which is validated in save()).
However, it seems that many people stumble upon this issue. Maybe an explicit note could be added to the documentation for the choices parameter?
This is because of backwards compatibility (and probably performance considerations).
There are ways to change the behavior in your project.
OK, thank you for the direct link. We will consider using this approach in our project.