Don't change your password while running freebsd-update

I found out the hard way today that freebsd-update doesn't like it when you change certain files while it's running. In retrospect, this makes sense; initially, I was a bit startled.

$ sudo sh freebsd-update.sh -f freebsd-update.conf -r 6.3-RELEASE upgrade
Looking up update.FreeBSD.org mirrors... 1 mirrors found.
Fetching metadata signature for 5.5-RELEASE from update1.FreeBSD.org... done.
Fetching metadata index... done.
Fetching 2 metadata patches.. done.
Applying metadata patches... done.
Inspecting system... done.

The following components of FreeBSD seem to be installed:
src/base src/bin src/contrib src/crypto src/etc src/games src/gnu
src/include src/krb5 src/lib src/libexec src/release src/rescue src/sbin
src/secure src/share src/sys src/tools src/ubin src/usbin world/base
world/compat20 world/compat21 world/dict world/doc world/manpages

The following components of FreeBSD do not seem to be installed:
world/catpages world/compat1x world/compat22 world/compat3x
world/compat4x world/games world/info world/proflibs

Does this look reasonable (y/n)? y

Fetching metadata signature for 6.3-RELEASE from update1.FreeBSD.org... done.
Fetching metadata index... done.
Fetching 1 metadata patches. done.
Applying metadata patches... done.
Fetching 1 metadata files... done.
Inspecting system... done.
Fetching files from 5.5-RELEASE for merging... done.
Preparing to download files...
File changed while FreeBSD Update running: /etc/master.passwd$

Whoops. Had to start all over again.