Distinct On not working with nested field?

I'm trying to use the Distinct on feature in a nested field Query is below
No matter what I try, there are non-distinct "zoneid" returning..it doesnt' seem to be working

Am I missing something or is this a bug??

query MyQuery {
tabledata: schema_1_tbl_7(where: {field_3_join: {tbl_6_id: {_is_null: false}}}) {
field_3_join(distinct_on: zoneid, order_by: {zoneid: asc}) {
tbl_6_id
zoneid
}
}
}

Start by reproducing the supplied MyQuery against the reported schema and inspect the nested field results for repeated zoneid values. Compare the observed behavior with the documented distinct_on semantics; the issue is done when the cause and expected behavior are established and a focused fix or clarification can be verified.

Written by the indexing model from the issue text.