PHP-Security - User login, and see someone else profile

hi everybody,

I'm developing a system using Code Ignitor framework.
When a user login to the system, it keeps user profile in session

as general way.

Sometimes users report me that, they can see "someone else

profile", and when change page, it becomes normal, and some times,
they can see someone else profile again. These users use their own

computer and not share to anyone.

This problem is found only some times, but it is really not good.
I cannot specify the cause, because session system in the

framework should be well-design.
I also wonder that for systems those require high-certainty such

as online banking, how do they manage this issue.

Please give me some idea about this problem.

Thanks a very lot,

We need a lot more information than this, unfortunately. Start logging session data along with IP, see if the session for an IP changes at random.