Django 1.7 filter Q m2m bug

[Grafumbly]

The behavior of Q objects has changed in an undocumented and breaking way for m2m relationships in Django 1.7 from the behavior in 1.6.7, returning different query results depending on the Django version.

In the case where you want to select a primary object that has related objects of one type, but none of another, you could use a Q like this:
q = Q(Q(relatedobject__someparam=True), ~Q(relatedobject__someparam=False))
results = PrimaryObject.objects.filter(q)

Using this Q in a filter in 1.6.7 would give you all primary objects that have relatedobjects with someparam=True and omit any primary objects that also had a relatedobject with someparam=False. In 1.7 these objects are returned despite the ~Q(relatedobject__someparam=False).

This gist provides a sample to illustrate the problem:
​https://gist.github.com/scottsexton/375f7869839a98593695

[Tim Graham]

It would be helpful if you could create a test for Django's test suite that demonstrates the issue (ideally reusing existing models if you can find appropriate ones) and bisect to the commit that introduced the regression.