A weird XFree86 problem!

[Sergey Niunco]

Hello,
 I posted this message a week ago, with no replies so far. Hopefully I'll get some replies this week.
 Here's the problem: 
I've recently tried to start 2 X sessions from 2 virtual terminals - one as unprivileged user and one as root. 
It went just fine the first time. Then I quit the "root" session and tried to start it again (while still running
another session as user). This time, however, the system went into reboot without any warning.
I assume this shouldn't happen, but I don't know where to start looking for a solution. 

I'm using XFree86-4.3.0, Nvidia drivers 1.0.3203 from ports
The system is: FreeBSD 4.8-RC #0: Thu Mar 20 02:34:57 CET 2003

What additional information do i need to provide and is it the right list to post this question?

 TIA.
   Sergey