memcached crashes after adding a 1.8 node to 1.7.2 cluster

CRASH REPORT <0.2436.0> 2011-12-05 10:48:27
===============================================================================
Crashing process
   initial_call {mb_master,init,['Argument__1']}
   pid <0.2436.0>
   registered_name mb_master
   error_info
         {exit,{{case_clause,true},
               [{mb_master,higher_priority_node,3},
                {mb_master,candidate,2},
                {gen_fsm,handle_msg,7},
                {proc_lib,init_p_do_apply,3}]},
              [{gen_fsm,terminate,7},{proc_lib,init_p_do_apply,3}]}
   ancestors [ns_server_sup,ns_server_cluster_sup,<0.52.0>]
   messages []
   links [<0.118.0>,<0.2260.0>,<0.49.0>]
   dictionary []
   trap_exit true
   status running
   heap_size 2584
   stack_size 24
   reductions 746