Backup of cluster throws error when there is rebalance in progress.

1. Load 1M documents into a cluster. Keep a background load running throughout
2. Rebalance in (or out) a node into the cluster
3. While the rebalance is in progress, start backup of the cluster.

The backup throws error saying not all items might have been backed up.

While taking backup while nodes are being removed, following error is seen:
Error backing up cluster: Not all data was backed up due to connectivity issues. Check to make sure there were no server side failures during backup. See backup logs for more details on what wasn't backed up.
Subsequently, while a node is being added and backup is taken, following error is seen (Same is the case while doing a swap rebalance):
Error backing up cluster: Partial backup error 2016-05-18T03_41_03.585492845-07_00