Child Aggregation with Parent Bucket Requires Execution Hint for Global Ordinals

Hi,

I have created a Parent Child relationship and I am executing aggregation queries.

My aggregation does not have a parent bucket, in which case, my counts do not match with the actual numbers ONLY for the children-level aggregations. Any other parent aggregations or children-within-parent-buckets work good. If I enable the execution hint of global ordinals on this aggregation, then my counts match. Is this documented behavior? I am using 1.4.2. I saw something relevant @ https://github.com/elastic/elasticsearch/issues/9271