[CentOS] System hangs at "Rebooting System" on VIA KM400 chipsets

Hello,

We have a number of systems running KM400 chipsets from VIA (Socket 
A/462).  Two different models have produced the same results -- DFI 
KM400-MLV and MSI KM4M-V.  When a /sbin/reboot or /sbin/shutdown -r now 
is issued, the system does everything you would expect from a reboot, 
but when it gets to Rebooting System, it hangs and requires a power cycle.

The logs do not indicate anything is going wrong.  It's not a kernel 
panic.  I've tried appending "acpi=off noapic" or just "apci=off" to 
grub.conf and neither help.  We've tested these boards extensively with 
various CPU's, hard drives, and RAM and they show no other issues, so 
it's not hardware defects or hardware compatibility issues.

I'm not sure what is going on, but assistance would be greatly appreciated.

Thanks.