Problem resolved, in case anyone is interested:
The resolution was to also bind the original vmk port to a nic. Once I had discovered that this solved the problem, logic dictated the creation of a second vmk port to be bound to the other nic connected to the vswitch. So I now have 4 vmk ports servicing two iSCSI VLANs - time to move the old storage on to the new iSCSI network.
