[CentOS] mismatch_cnt after 5.3 -> 5.4 upgrade

Saturday I did an upgrade from 5.3 (original install) to 5.4.  Saturday
night, /etc/cron.weekly reported the following:

       /etc/cron.weekly/99-raid-check:

       WARNING: mismatch_cnt is not 0 on /dev/md0

md0 holds /boot and resides, mirrored, on sda1 and sdb1. md1 holds
an LVM volume containing the remaining filesytems, including swap.

The underlying hardware is just a few months hold, has passed the
usual memtest stuff, and has been running 5.3 well for a few months.

I'm *guessing* that due to the timing, this is related to the upgrade.
I have to admit that I forgot myself and instead of doing the glibc
updates as recommended, I only did:

	yum clean all
	yum update yum		  
	rpm -e --nodeps perl-5.8.8-18.el5_3.1.i386
		(see today's perl thread)
	yum update perl.x86_64
	yum update
	shutdown -r now

I've taken a backup of /boot dump after the upgrade, but have not yet
reenabled normal backups.

My hunch is that something in the upgrade process touched sda1 but not
sdb1, and that removing sdb1 from the mirror and reattaching it for 
resync would be sufficient, however I was looking for comments on this
from anyone with experience or opinion on the matter.  Googling the
issue doesn't seem to turn up any recent related results.

Also, could the upgrade have touched the bootblock on sda1 but not 
sdb1 and thus trigger this problem?

Devin
-- 
A zygote is a gamete's way of producing more gametes.  This may be the
purpose of the universe.				- Robert Heinlein