spurious reboots

[manu%netbsd.org@localhost (Emmanuel Dreyfus)]

Hello

I have an amd64 box that worked fine with NetBSD 4. Since I upgraded it
to NetBSD-5, it now exhibit spurious reboots, with the following
characteristics:
- building a few packages will reliabily cause the reboot within a few
minutes
- it never happens when the machine is idle
- there is no panic, no console message at all. It just reboots. 
- ddb.onpanic is set to 1
- I tried a kernel without ACPI, it does not change the behavior

Any idea?

-- 
Emmanuel Dreyfus
http://hcpnet.free.fr/pubz
manu%netbsd.org@localhost