diskless vkernel: corrupted files after "pkg_admin check"

[Rumko]

After pkg_admin check is run (part of daily cronjobs) many files get corrupted
(/var/db/pkg, /etc, probably other dirs affected as well).
All the files are still there and the same size, but e.g. cat outputs nothing
while with vi, many "^@" can be seen instead of the expected content.

It seems this happens only on tmpfs mounts, while files on the nfs mount do not
seem to be affected at all.
Have been trying to repeat the behaviour on a physical box, but was unable to
repeat it, it seems only vkernels are affected by this.
-- 
Please do not CC me, since I already receive everything from these MLs.

Regards,
Rumko