5.1-BETA i386 spontaneous reboot?

Hi,

I've just had a machine running

FreeBSD buffy.york.ac.uk 5.1-BETA FreeBSD 5.1-BETA #0: Wed May 14
11:15:54 BST 2003 i386

spontaneously reboot on me. I was running screen (as a normal user)
remotely, running "pkg_add -r wget"  (as root)and (as a normal user)
moving a folder from an NFS mounted filesystem to a local disk when the
machine rebooted. Nothing was left in the log file other than the
machine coming back up, and the machine never produced a crash dump.

The machine may have paniced before rebooting as I do have
DDB_UNATTENDED in the kernel, but for whatever reason a dump was not
saved and no evidence of a panic is in the messages log. I believe the
hardware is healthy.

I know this is far too vague to be useful, and I don't think there is
any other information I can ofer, but I thought I should report it
anyway.

Gavin