BUG #16976: server crash when deleting via a trigger on a foreign table

The following bug has been logged on the website:

Bug reference: 16976
Logged by: Herwig Goemans
Email address: herwig(dot)goemans(at)gmail(dot)com
PostgreSQL version: 12.6
Operating system: ubuntu 18.04
Description:

Hello,

I have experienced a server crash when deleting from a table that ahs a
before trigger on it. The before trigger calls a function that deletes from
a foreign (informix) table.
The table in PG:
CREATE TABLE metadblucht.c_eenheid (
enh_id serial NOT NULL,
dat_wijziging timestamp NOT NULL,
gebr_wijziging varchar(255) NULL,
CONSTRAINT pk_enh PRIMARY KEY (enh_id)
);
Trigger and function:
create trigger td_c_eenheid before
delete
on
metadblucht.c_eenheid for each row execute function pd_c_eenheid();
create trigger ti_c_eenheid before
insert
on
metadblucht.c_eenheid for each row execute function pi_c_eenheid();
create trigger tu_c_eenheid before
update
on
metadblucht.c_eenheid for each row execute function pu_c_eenheid();


CREATE OR REPLACE FUNCTION metadblucht.pd_c_eenheid()
RETURNS trigger
LANGUAGE plpgsql
AS $function$
BEGIN
delete from informix.t_water_eenheid
where enh_id = new.enh_id;
END;
$function$
;
foreign table:
CREATE FOREIGN TABLE informix.t_water_eenheid (
enh_id int4 NOT NULL
)
SERVER o_oltp_app_water
OPTIONS (table 'c_eenheid_metadblucht', database 'water', client_locale
'en_US.utf8', db_locale 'nl_be.utf8');

The statement causing the server crash:
start transaction;
delete from metadblucht.c_eenheid where enh_id = 40;

If I do a delete directly on the foreign table it works fine:

start transaction;
delete from informix.t_water_eenheid where enh_id = 40;
rollback;

This is the relevant section in the PG log file:
__2021-04-21 11:54:30 CEST LOG: server process (PID 3933) was terminated by
signal 11: Segmentation fault
__2021-04-21 11:54:30 CEST DETAIL: Failed process was running: delete from
metadblucht.c_eenheid where enh_id = 40
__2021-04-21 11:54:30 CEST LOG: terminating any other active server
processes
gebouwenbeheerdba_gebouwenbeheer_2021-04-21 11:54:30 CEST WARNING:
terminating connection because of crash of another server process
gebouwenbeheerdba_gebouwenbeheer_2021-04-21 11:54:30 CEST DETAIL: The
postmaster has commanded this server process to roll back the current
transaction and exit, because another server process exited abnormally and
possibly corrupted shared memory.
gebouwenbeheerdba_gebouwenbeheer_2021-04-21 11:54:30 CEST HINT: In a moment
you should be able to reconnect to the database and repeat your command.
oari_ari_2021-04-21 11:54:30 CEST WARNING: terminating connection because
of crash of another server process
oari_ari_2021-04-21 11:54:30 CEST DETAIL: The postmaster has commanded this
server process to roll back the current transaction and exit, because
another server process exited abnormally and possibly corrupted shared
memory.
oari_ari_2021-04-21 11:54:30 CEST HINT: In a moment you should be able to
reconnect to the database and repeat your command.

I hope someone can help.
Thanks.