duplicate items returned from treeitem query

Posted on behalf of Ricardo Signes. Original posting date 2018-06-14.

I'm issuing this request:

  my $uri = "/treeitems/?filter[]=package_id=$PKG_ID"
          . "&filter[]=is_done is false"
          . "&flat=true"
          . "&item_type is Task"
          . "&owner_id=$member_id";

…and the array of items that I get back contains each tree item exactly twice. That is, item 1234 appears two times in the JSON array, as does item 2345, etc.

I can suppress a duplicate result as well as the next person, but why is this happening?