Rebalance did not fully Rebalance, allowing another Rebalance (add and rebalance did not succeed)

extracted from comments from MB-1332...

build 1.6.0beta1-2

sent rebalance+add

node was added but cluster was not rebalanced

[root@domU-12-31-39-18-36-10 cli]# ./membase rebalance
--cluster=10.104.109.242:8080 --server-add=10.254.38.176:8080
SUCCESS: server added..

[root@domU-12-31-39-18-36-10 cli]# ./membase server-list -c 10.104.109.242:8080
ns_1@10.104.109.242 healthy
ns_1@10.214.126.144 healthy
ns_1@10.254.38.176 healthy

at this point the web UI (all three machines) shows a message
Fail Over Warning: Your system is missing replicants until you rebalance.

also, find out if there are any vbuckets on the newly-added machine (there
are not)
./vbucketctl.py 10.104.109.242:11210 list > ~/mach1-bucketList
--> results in what seems to be a list of all 256 vbuckets
./vbucketctl.py 10.254.38.176:11210 list > ~/machC-bucketList
--> empty file

then, run rebalance command alone
./membase rebalance -c 10.104.109.242:8080

this succeeeds

i.e., issue appears to be when running the process in one fell swoop using
membase rebalance