Adding a node to the cluster while rebalancing cause the rebalance to abort

Add a node to the cluster, and start rebalance. While rebalance is running try to add a third node to the cluster. Adding the node cause the ongoing rebalance to fail with a red banner on the web ui saying:

"Rebalance failed. See logs for detailed reason. You can try rebalance again."

I was expecting the rebalance to complete with the two nodes I've started the rebalance operation. And then let me rebalance in the next one when it was done (or let me press stop rebalance in the UI to start the new rebalance with all of the 3 nodes).

There is no "easy to understand" error message in the log that my mum would have understood (it is a: Rebalance exited with reason {detected_nodes_change,
{ns_node_disco_events,
['ns_1@10.0.0.130','ns_1@10.0.0.159'],
['ns_1@10.0.0.130','ns_1@10.0.0.159',
'ns_1@10.0.0.160']}}

But if this is a normal case we could probably rewrite the message into something more intuitive for users (given that we pointed them to the log to see why it failed...)