JSON path query returns duplicate values

Hello,

I wonder why this query

   select jsonb_path_query_array(col, '$.**.itemName')
   from (
     values ('{"items": [{"itemName": "a", "items": [{"itemName": "b"}]}]}'::jsonb)
   ) as t(col)

returns each itemName twice: ["a", "a", "b", "b"]

I would have expected: ["a", "b"]

Thomas