Rebalance failed after remove node

Download ns server 1.6.0beta3.1 for windows from NorthScale website and
install it on 2 window 7 64bit (call A and B)
On node A, default bucket size is 1 GB.
On node B, default bucket size is around 3.1 GB.
Add node B to node A
Rebalance is ok (as expected)
On node A on server page, click "Remove Server" to remove node B.
Click "Rebalance" to rebalance the cluster.
Rebalance failed. Try to reload the page but "Rebalance" button still clickable.
http://screencast.com/t/MTZiMDVlN
I still see node B in node B but actually node B is out already.
Check on node B, reload the page and it goes to initial setup page.
Try to rebalance on node A one more time, the page reloads with error.
http://screencast.com/t/NzkzZWVh
http://screencast.com/t/ZGY3MTI4N2U
Here is the capture of log page.
http://screencast.com/t/M2Q4NjJkZTIt