Further to the above - I figured that there must be some serious issue in my setting up of the MDs. Every time a new one is added or rebuilt two things happen - first the symlinks go awry and I have to repair it:
in /usr/pluto/diskless/99/ both the initrd.img and vmlinuz symlinks get stuffed for some reason, and fixing it gets everything humming along again.
and secondly /etc/exports get changed and I have to modify it -
From:
/usr/pluto/diskless/99 192.168.80/255.255.255.0 eth0(rw,no_root_squash,no_all_squash,sync,no_subtree_check)
To
/usr/pluto/diskless/99 192.168.80.3/255.255.255.0 eth1(rw,no_root_squash,no_all_squash,sync,no_subtree_check)
If anyone can offer some intelligence here I'll be very happy!