OSPFv3 auth problem

We have a ring of routers(5 of them) running unnumbered pppoe links between them. Adding OSPF authentication (auth trailer) works OK. However, removing OSPFv3 on ONE interface causes big problem in some cases, we loose auth in the whole ring and routing is then kaputt for all routers. We have noted that some PDUs(like LS update) are sent without auth trailer so the receiving nodes complains with "ospfv3_2: Authentication failed for nbr 0.0.139.1 on p1-1-3-1-4 - missing authentication trailer (0)" OSPFv3 Hello is OK though, it still has its auth trailer. Any ideas? Jocke