filter and chained zfilter prevent filter to be applied

[kiddouk]

This code:

obj.filter(obj_ref_id=1).zfilter(count__in=(1, 20)) is not executed properly. Only the zfilter is apply, leaving the filter on the object reference out.

The code documentation states that only one zfilter will be applied due to performances issue but the previous filter is not applied and should.