XDCR data loss after rebalance out

Setup
--------
3*2 clusters, bi-xdcr on default bucket.
C1 = [.186, .187, .190]
C2 = [.188,.189]

Scenario
------------
1. Load 20K items onto cluster1, another 20K items onto cluster2.
2. In parallel, rebalance out 2 nodes from source.
3. Compare item count, data and meta-data

Testcase
-------------
./testrunner -i bixdcr.ini get-cbcollect-info=True,get-logs=False,stop-on-failure=False,get-coredumps=True -t xdcr.rebalanceXDCR.Rebalance.async_rebalance_out,items=20000,rdirection=bidirection,async_load=True,ctopology=chain,expires=60,rebalance=source,num_rebalance=2

Missing keys
------------------
Source : 40000
Destination: 39996

4 missing keys on C2 (loaded at C1) :

<

{"id":"loadOne2203","key":"loadOne2203","value":"1-002a5bb5180aa2e80000000000000000"}

,
<

{"id":"loadOne2393","key":"loadOne2393","value":"1-002a5bb5607520d90000000000000000"}

,
<

{"id":"loadOne2571","key":"loadOne2571","value":"1-002a5bb58ef3ddb40000000000000000"}

,
<

{"id":"loadOne4133","key":"loadOne4133","value":"1-002a5bb86fbcdc440000000000000000"}

,

Attached
------------
1. cbcollect with xdcr trace logging
2. data files

Consistent?
----------------
No, reproduced 2 on 6 times.