Bug in psql (\dd query)

Hello,

I was checking for way to get object comments, and it seems that \dd has
bug when it comes to extracting descriptions for constraints. Relevant
part of query psql is executing is:

SELECT DISTINCT tt.nspname AS "Schema", tt.name AS "Name", tt.object AS
"Object", d.description AS "Description"
FROM (
   SELECT pgc.oid as oid, pgc.tableoid AS tableoid,
   n.nspname as nspname,
   CAST(pgc.conname AS pg_catalog.text) as name,  CAST('constraint' AS
pg_catalog.text) as object
   FROM pg_catalog.pg_constraint pgc
     JOIN pg_catalog.pg_class c ON c.oid = pgc.conrelid
     LEFT JOIN pg_catalog.pg_namespace n     ON n.oid = c.relnamespace
WHERE n.nspname <> 'pg_catalog'
       AND n.nspname <> 'information_schema'
   AND pg_catalog.pg_table_is_visible(c.oid)
    /* more unions here */
) AS tt
   JOIN pg_catalog.pg_description d ON (tt.oid = d.objoid AND
tt.tableoid = d.classoid AND d.objsubid = 0)
ORDER BY 1, 2, 3;

obviously it is trying to get description for (table_oid,
constraint_oid, 0), while in fact it should read description for (oid of
pg_catalog.pg_constaint, constraint_oid, 0).

At least last tuple is what comment statement is inserting into
pg_description table

Regards,
Ivan