It seems that NFS exports over IPv6 don't work (the mount fails with
EPERM) if the exports file (or the netgroup) lists a host by a name
which corresponds to both an IPv4 and IPv6 address. Only once I
explicitly add the IPv6 address literal (either in /etc/exports or
/etc/netgroup) it works.  Is this a known issue or am I doing something
wrong?

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert      -- You author it, and I'll reader it.
\X/ rhialto/at/xs4all.nl        -- Cetero censeo "authored" delendum esse.