Multiple sessions makes OTRS sluggish

[Sofia]

I'm posting this in 'Errors' as I consider this to be more of an error than a configuration question.

We are running OTRS in production since summer 2012 and except for some prestanda issues it has worked perfectly.
I have been troubleshooting and elimiating each prestanda error one by one, but there are a few more left that I can't figure out and the major is with sessions;

We have a handful of users and - appearantly without any reason - sometimes a new session is created for any user. This leaves us with multiple sessions per users.
We have tried to identify when this happens but can't find any particular reason but it almost seems random. When this happens, the system is getting more and more sluggish for everyone working in it and sometimes it stops completely in the end. In 95% of the cases multiple sessions can be identified and killing the oldest ones so only one session per user remains resolves the problem. In the other 5% the services needs to be restarted as well.

In order to - partly - get around this, we have configured the sessions to automaticlly end if they are open more than 90 minutes without activity. It has reduced these issues somewhat but they still remain.
We have tested to use both SessionID and cookies as the sessiontracker but it does not seem to have any effect on the situation, except that cookies seems somewhat more stable.

Question-
- Is it possible to automatically configure a session to end if a new one i established for the same user?

Any ideas or input would be much appreciated.