BUG #13506: jsonb || operator does not work

The following bug has been logged on the website:

Bug reference:      13506
Logged by:          Grégoire HUBERT
Email address:      gregoire.hubert@pragmafabrik.com
PostgreSQL version: 9.5alpha1
Operating system:   debian jessie
Description:

select val->'a'||val->'c' from (values ($j${"a": {"b": 2}, "c": {"d":
3}}$j$::jsonb)) a (val);
┌──────────┐
│ ?column? │
├──────────┤
│ {"d": 3} │
└──────────┘
(1 row)

I think this should return '{"b": 2, "d": 3}'