MBR zapped when panicking?

Hi,

Today I had a -CURRENT machine panic on me with a page fault, and
something happened that I have seen before: the machine refused to
come up afterwards. Closer inspection revealed that the MBR on the
boot disk was totally zapped, filled with seemingly random characters.
Luckily the disk label was still intact, allowing me to recover the
machine reasonably easy. The MBRs on the other disks (see attached
dmesg.txt for more info) wasn't touched by the panic.

Note that all disks in this machine are Dangerously Dedicated (see
attached fdisk-ad[023].txt). I hope that's not totally unsupported,
but what I do observe is that all these DD partitions seem to start at
offset 0 instead of 1, thereby making the MBR actually part of the
partition itself. Could this be a reason for something (GEOM?)
stomping over the MBR when the box panics?

Btw, this panic was a page fault, and I got the nice 'giving up on xxx
buffers' message too... :(  It seems to have panicked somewhere in the
IPv6 stack (see panic.txt for more info), I think I read somewhere
that this has been fixed already? If so, I'll just cvsup and hope it
doesn't happen again...

Anyhow, I'll be keeping some extra spare backups of all my bootsectors
and disklabels. :)

Cheers,
Dimitry