PostgreSQL Bug with simple function unexpectedly treating varchar parameter as an array

[Rumpi Gravenstein]

PostgreSQL Experts,

I've been confound by the following behavior that I see in one of our
PostgreSQL 16 instances.  In this case I am running this script from psql.

---------------------------------------------------------------------------------------------------------
xxxx_pub_dev_2_db=# SELECT version();
                                                 version
---------------------------------------------------------------------------------------------------------
 PostgreSQL 16.9 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0
20210514 (Red Hat 8.5.0-26), 64-bit
(1 row)

xxxx_pub_dev_2_db=# SHOW server_version;
 server_version
----------------
 16.9
(1 row)

xxxx _pub_dev_2_db=# DROP FUNCTION if exists _sa_setup_role;
DROP FUNCTION
xxxx _pub_dev_2_db=# CREATE OR REPLACE FUNCTION _sa_setup_role(
p_role_to_be_granted varchar)
xxxx _pub_dev_2_db-# RETURNS varchar
xxxx _pub_dev_2_db-#     LANGUAGE plpgsql
xxxx _pub_dev_2_db-# AS
xxxx _pub_dev_2_db-# $function$
xxxx _pub_dev_2_db $# declare
xxxx _pub_dev_2_db$# begin
xxxx _pub_dev_2_db$# raise info '%',p_role_to_be_granted::varchar;
xxxx _pub_dev_2_db$#   return('Done');
xxxx _pub_dev_2_db$# end;
xxxx _pub_dev_2_db$# $function$;
CREATE FUNCTION
xxxx _pub_dev_2_db=# select _sa_setup_role('af_repo_app');
ERROR:  malformed array literal: "af_repo_app"
LINE 1: select _sa_setup_role('af_repo_app');
                              ^
DETAIL:  Array value must start with "{" or dimension information.
xxxx _pub_dev_2_db=# select _sa_setup_role('af_repo_app'::varchar);
INFO:  af_repo_app
 _sa_setup_role
----------------
 Done
(1 row)

I've been able to run the same script with no issues in other PostgreSQL
databases, just not this one.

Thoughts?

Here's the script:

SELECT version();

SHOW server_version;

DROP FUNCTION if exists _sa_setup_role;

CREATE OR REPLACE FUNCTION _sa_setup_role( p_role_to_be_granted varchar)

RETURNS varchar

LANGUAGE plpgsql

AS

$function$

declare

begin

raise info '%',p_role_to_be_granted::varchar;

return('Done');

end;

$function$;

select _sa_setup_role('af_repo_app');

select _sa_setup_role('af_repo_app'::varchar);

Best Regards
-- 
Rumpi Gravenstein