*.pst and additional mailbox are gone after another person used my

In Outlook I added a personal folder and an additional mailbox on which I
have the appropriated permissions. The *.pst file is for sure stored in my
User data directory on a network share on which I also have the appropriated
permissions.I have double checked there is no reference to a local drive for
the *.pst Each day I log on and off. So far no problem. However if I logon
after a colleague of my has used my computer, my *.pst and additional mailbox
are gone. The connection to my main mailbox is still present.

So I have to add again the personal folder and the additional mailbox. What
causes this problem and more important how can I prevent this. This problem
occurs by several people but not to all. I have tried to reproduce the
problem with a test account but as usually this is working fine.

I have captured the HKCU\Software\Microsoft\Windows
NT\CurrentVersion\Windows Messaging Subsystem and this shows that the *.pst
file is bounded at moment off logon. So this is also very strange.