After up2date, MBR is gone... is this possible?

[David Tonhofer, m-plify S.A.]

And another one: I'm currently trying to rebuild a server that
had its /boot partition blown away (some trouble with the md
devices, I reckon). I reinstalled a RH ES 4.0 from scratch and
copied the old salvaged /etc/syconfig/rhn/systemid file into the
new installation to keep the license for that machine alive. I
did not copy the rhn-uuid though. After that I ran up2date to
get the latest updates and kernel images. Then I rebooted. The
end result was that the MBR of the first harddisk was wiped clean
(hot surprise!) so I'm currently doing a 'take two' at reinstallation. Is this a problem with my machine or Red Hat enforcing their licensing  terms (which I suppose would not be the
case, but I'm paranoid)?

Best regards,

-- David