after failover a node, memcached crashed with exit status 71 on leaving node

Install couchbase server 1.8.1-840 on 10 centos 5.x servers 64bit
Create a 10 nodes cluster with 6.5 GB default bucket.
Load 30 million items with 256 bytes/item and 10 million items with 512 bytes/item
Cluster goes in to dgm with 78.8 % resident ratio
Mutate 40 million items to create cache miss and disk fetch. Maintain the load around 15K to 17K ops.
Add a node (54) to cluster and rebalance
Add another node (55) to cluster and rebalance
Remove node 54 and failover node 55. Then rebalance.
At failover node 55, memcached crashed on node 55
Error:
Port server memcached on node 'ns_1@10.3.2.55' exited with status 71. Restarting. Messages: failed to listen on TCP port 11211: Address already in use (repeated 5 times)