Instability on Raspberry Pi

[Sevan / Venture37]

Hi, 
I have my rpi loading the kernel via an sd card & root via another SD card in a USB adapter, /usr/ports is mounted via NFS, im using the R-PI kernel conf with nfs client enabled & rootdevice declared.
Im getting between 30 to 40 mins uptime before the system hangs, consistent reproducible test is attempting to build pcre from ports, I thought I was running out of RAM but this turned out to be not true, system with a swapfile configured & 10MB RAM free still hung.
Kernel was built from src updated last night (r241055)

Sevan