Unwanted Session duplication in Django

Question

We're using cached_db as our SESSION_ENGINE. We have a session duplication issue, this is the scenario:

1. User 1 is browsing the system.
2. User 2 is browsing and modifying his session.
3. User 1 continuing browsing and finds that his session changed to User's 2 session.

If we use SESSION_SAVE_EVERY_REQUEST then it works fine but we want to fix this problem from the source.

We are using Django 1.6 with Redis