[ic] Session always changes after first access

[Grant]

I can see from my logs that a visitor's session always changes after
the first page is accessed.  This looks like:

access1 - session1
access2 - session2
access3 - session2
access4 - session2

Does anyone have any idea what might be causing this or where I might
look to try and find out?  I am using:

ScratchDefault mv_no_session 1

in catalog.cfg so I require cookies, but the session seems to change
after the first access whether a user has cookies enabled or not.

- Grant