Hi there, I completely missed that this had caused so much interesting discussion. I've added a regression test that shows the bug I was encountering, which seems to be related to 
 spec_set bypassing _Call's overwritten __eq__ and so not respecting ANY https://github.com/python/cpython/pull/14700

I agree, this is definitely also a third party bug with Django, but I think it's a problem here too, and am working on a fix.