SIGHUP on tty while logging in

I am using a serial port (ttyS0) for my console and 
whenever I "cu" into the port and get a login prompt, I sometimes get 
a SIGHUP right after entering the user name, thus resulting 
in my being disconnected before I get a chance to complete login. 
It is random. Sometimes login proceeds with no problem and 
sometimes I get the SIGHUP during login. 
This happens even when I do not configure
my kernel to use my serial port as a console and I just
cu into the port and login. 

Has anyone else experienced this? One of my machines
is linux-2.5.58 and the other is 2.5.59. It happens on both.

My tty settings look ok and it is not my getty applications. I tried 
agetty and mgetty and I got the same results. I am wondering if it is
the driver... 

Thanks,
Joy