Json facets in range dates do not mantain the order across multiple shards

I have multiple shards and when I make a range facet in a date field across the shards, it does not respect the order. That is, making a request with gap +1YEARS across the shards 2012_collection, 2013_collection, 2014_collection the response put 2013 first, then 2012, and then 2014 (for example). I tried making it with +1MONTHS and it respect the order within each shard, but not in a global way.