XDCR error: "database out of sync" seen on source after there's been a cluster change (failover/rebalance) on the destination

c1: 10.1.3.237, 10.3.2.54, 10.3.121.126
c2: 10.1.3.238, 10.3.2.55, 10.3.121.127

default: c1 --> c2

• Load 10K items on c1, items replicate to c2.
• Failover a node (10.3.2.55) on c2, add back, then rebalance
• Failover a node (10.3.121.127) on c2, rebalance.
• Add node 10.3.121.127 to c2, rebalance

• Add more items on c1.
• Xdcr error (continuously) seen on c1:
  2012-11-27 17:09:13 - Error replicating vbucket 602: <<"Target database out of sync. Try to increase max_dbs_open at the target's server.">>