Read-only /usr/obj/ no longer kosher?

I used to build world and kernel on one machine and export both /usr/src/ and
/usr/obj read-only to other machines. It doesn't work anymore (this is from
'make installworld'):

===> bin/freebsd-version (install)
eval $(egrep '^(TYPE|REVISION|BRANCH)=' /usr/src/bin/freebsd-version/../../sys/conf/newvers.sh) ;  if ! sed -e " s/_at__at_TYPE_at__at_/${TYPE}/g;  s/_at__at_REVISION_at__at_/${REVISION}/g;  s/_at__at_BRANCH_at__at_/${BRANCH}/g;  " /usr/src/bin/freebsd-version/freebsd-version.sh.in >freebsd-version.sh ; then  rm -f freebsd-version.sh ;  exit 1 ;  fi
cannot create freebsd-version.sh: Permission denied
rm: freebsd-version.sh: Read-only file system
*** Error code 1

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
FreeBSD committer                         http://www.FreeBSD.org
Am I Evil? Yes, I Am!                     http://mobter.com