UNION of federated sources are returning results like UNION ALL in EDS

Issue

• The UNION of two or more federated sources are producing the wrong results and behaving like UNION ALL instead.

select <col1> from <schema>.<table1> where <col2> = 'X' and <col1> = 'Y'
union
select <col1> from <schema2>.<table2> where <col2> = 'X' and <col1> = 'Y'
union
select <col1> from <table3> where <col1> = 'Y'

• expect to see 1 record but the query is returning 2 records.