Double NFS mount causes panic?

[cpghost]

After upgrading my diskless setup from 5.4 to RELENG_6, the
diskless clients now panic when calling mount_nfs on directories
that have already been mounted via NFS in a previous step. Of
course it revealed a bug in my setup, but is it expected to
panic when double NFS-mounting over an NFS-mounted directory?
I thought a new mount would simply mask the mount below as
with regular mounts?

6.0-STABLE FreeBSD 6.0-STABLE #0: Wed Jan 25 20:50:14

Thanks,
-cpghost.

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