RowDescription for a function does not include table OID

I am working on a meta-programming use-case where I need to scrape some detailed information about the results of a function that "RETURNS TABLE (LIKE physical_table)", which ends up with prorettype = 'physical_table'::regtype.

The problem is that for the query "SELECT * FROM my_function()" the RowDescription that is sent back shows 0 for Table OID and Column Index.

From Wireshark:

PostgreSQL
    Type: Row description
    Length: 219
    Field count: 7
        Column name: table_id
            Table OID: 0
            Column index: 0
            Type OID: 20
            Column length: 8
            Type modifier: -1
            Format: Binary (1)
<snipped>

I would expect that the Table OID contains the relation OID of this table, as it would do for a typical statement like "SELECT * FROM my_table". It would seem there is a bug here that is preventing PostgreSQL from connecting the dots.

Regards,

Maxwell.