waiting for index update hangs

I was running rebalance out 4 -> 2 with default bucket of 420k small json items with single index. And rebalance got stuck due to waiting for index to be updated.

After sending the following to diag/eval rebalance completed fine:

[begin couch_set_view:trigger_update(<<"default">>, <<"_design/t">>, 0), timer:sleep(200) end || _ <- lists:seq(0, 100)].