active and replica items show overflow in disk queue section after upgrade from 2.0.0 to 3.0.0-605

Install couchbase server 2.0.0 on 3 ubuntu server 12.04 64-bit (148, 149 and 150)
Create 2 buckets (default and sasl) with 1 replica
Load 10000 items into each bucket

Install couchbase server 3.0.0-605 to another ubuntuserver (151)
Do swap rebalance (add 151 into cluster and remove node 150)
See items overflow in both active and replica in disk queue section

Then uninstall couchbase server 2.0 on node 150. Delete couchbase default install path (/opt/couchbase)
Install couchbase server 3.0.0-605 to node 150
Do swap rebalance (add 150 into cluster and remove node 149)
Repeat again to remove node 148

When cluster is completely online upgrade to 3.0.0, I still see the overflow items in both active and replica in disk section