Asyncpg does not accept the usage of the operator - between a jsonb value and a text value

[rubik]

• asyncpg version: 0.18.3
• PostgreSQL version: 11.4
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: No
• Python version: 3.7.3
• Platform: ArchLinux
• Do you use pgbouncer?: No
• Did you install asyncpg with pip?: Yes
• If you built asyncpg locally, which version of Cython did you use?: N/A
• Can the issue be reproduced under both asyncio and
  uvloop?: uvloop is not relevant to the bug

It seems that asyncpg does not allow to use the operator - between a jsonb value and a text value. It is indeed possible, as documented here (fourth row from the bottom):
https://www.postgresql.org/docs/11/functions-json.html#FUNCTIONS-JSONB-OP-TABLE

The query that I am using is:

    UPDATE campaigns.campaigns
    SET stage_names = stage_names - $3, stages_order = stages_order - $3
    WHERE user_id = $1 AND id = $2;

Those two columns are defined as follows:

CREATE TABLE IF NOT EXISTS campaigns.campaigns (
    id              SERIAL PRIMARY KEY,
    user_id         INTEGER NOT NULL REFERENCES user_data.users(id),
    stage_names     JSONB NOT NULL DEFAULT '{"0":"X1","1":"X2","2":"X3","3":"X4"}',
    stages_order    JSONB NOT NULL DEFAULT '["0","1","2","3"]',
);

When I execute:

    await pool.execute(
        sql.REORDER_CAMPAIGN_STAGES,
        user['id'],
        campaign_id,
        str(stage_id),
    )

I get the following error:

  File "/lib/python3.7/site-packages/asyncpg/pool.py", line 509, in execute
    return await con.execute(query, *args, timeout=timeout)
  File "/lib/python3.7/site-packages/asyncpg/connection.py", line 275, in execute
    _, status, _ = await self._execute(query, args, 0, timeout, True)
  File "/lib/python3.7/site-packages/asyncpg/connection.py", line 1414, in _execute
    query, args, limit, timeout, return_status=return_status)
  File "/lib/python3.7/site-packages/asyncpg/connection.py", line 1422, in __execute
    return await self._do_execute(query, executor, timeout)
  File "/lib/python3.7/site-packages/asyncpg/connection.py", line 1444, in _do_execute
    result = await executor(stmt, None)
  File "asyncpg/protocol/protocol.pyx", line 178, in bind_execute
  File "asyncpg/protocol/prepared_stmt.pyx", line 160, in asyncpg.protocol.protocol.PreparedStatementState._encode_bind_msg
asyncpg.exceptions.DataError: invalid input for query argument $3: '1' (a sized iterable container expected (got type 'str'))

It seems asyncpg is expecting an array, when in fact a string is perfectly fine. I have tried working around the problem by changing the query to the following:

    UPDATE campaigns.campaigns
    SET stage_names = stage_names - ($3)[1], stages_order = stages_order - ($3)[1]
    WHERE user_id = $1 AND id = $2;

and the code to:

    await pool.execute(
        sql.REORDER_CAMPAIGN_STAGES,
        user['id'],
        campaign_id,
        [str(stage_id)],
    )

in the hope of making it work by supplying an array like asyncpg wants and then taking the first element. But this produces a completely wrong result and I'm not sure why.

All is fine in psql:

=# select stage_names - '1' from campaigns.campaigns where id = 1;
                       ?column?                        
-------------------------------------------------------
 {"0": "X1", "2": "X3", "3": "X4"}
(1 row)

=# select stages_order - '1' from campaigns.campaigns where id = 1;
    ?column?     
-----------------
 ["0", "3", "2"]
(1 row)

EDIT: The problem was totally unrelated to asyncpg.