Tested on Mongoid 3.1.4.

Currently all the indexes with the create_indexes task are create without the safe: true option. This means that, whenever my unique index fails to create because of the duplicate keys error, I see in the create_indexes logs, that the index was created, and I'm never going to know that there's in fact no index.

So I believe, that the create_indexes task has to create indexes with the safe: true option, or we can pass the safety value as an option to the task, or we can add the create_indexes_safely task.