FlexIndex: FTS index(with type mapping) returns 0 results for query:predicate with datetime comparison

It has been observed that below datetime fts index field type flex query with fts is not working.

• Flex using FTS queries with datetime index field : —> not working

  select meta().id, name,join_date from `default` USE INDEX (USING GSI, USING FTS) where type='emp' and join_date<'2015-08-13’

  select meta().id, name,join_date from `default` USE INDEX (USING FTS) where type='emp' and join_date<'2015-08-13’

  select meta().id, name,join_date from `default` USE INDEX (emp_type_index USING FTS) where type='emp' and join_date<'2015-08-13'

  Expected result: 978 rows (same as GSI query)
  Actual result: 0 rows (fts index search is happening as per the plan)

• Primary GSI index query: --> working as expected

  select meta().id, name,join_date from `default` where type='emp' and join_date<'2015-08-13’

  Expected result: 978 rows
  Actual result: 978 rows

• Dataset: Attached

• FTS index definition : attached.

• Test node: is below with Couchbase build: 7.0.0-1897 (regular creds)
  http://172.23.104.163:8091/ui/index.html#/query/workbench?scenarioBucket=default&scenarioZoom=minute