The cart is empty after the addition of goods using postgresql

[vivazzi]

django-shop-categories doesn't work for me. It's app is run but after the addition of goods the cart is empty. Then i see that if to use sqllite, then django-shop-categories is work very well! But if I use postgresql (version 9.1.9) my cart is empty.
I try to follow example https://github.com/fivethreeo/django-shop-example but i get same bug.