Invalid QuerySet count caching

[wojcikstefan]

Steps to reproduce:

class User(Document):
    name = StringField()

User.drop_collection()
User.objects.create(name='aaa')
User.objects.create(name='bbb')
User.objects.create(name='ccc')
qs = User.objects
print qs.count(with_limit_and_skip=True)  # 3
User.objects.create(name='ddd')
print qs.count(with_limit_and_skip=True)  # still 3 :(

Expected behavior: the 2nd count returns 4.
Actual behavior: the 2nd count returns 3, because the query set's previous count result is cached.