Test inserted text in trigger (arrays, custom types)

Hello people,

I tried to compose a header that sums up the question :).

Now to the actual question;

I do the following

DROP TABLE IF EXISTS mytable;
DROP TYPE IF EXISTS mytype;

CREATE TYPE mytype AS (
a_nr Numeric(18,7),
a_text Text
);

CREATE TABLE mytable(
id Serial NOT NULL PRIMARY KEY,
some_col mytype[] NOT NULL
);

CREATE OR REPLACE FUNCTION chk_mytab_input() RETURNS TRIGGER
LANGUAGE 'plpgsql'
VOLATILE
AS $BODY$
BEGIN
-- for all some_col
FOR c IN array_lower(NEW.some_col,1)..array_upper(NEW.some_ col,1) LOOP
RAISE INFO '%', (NEW.some_col[c]).a_text IS DISTINCT FROM 'VA';
RAISE INFO '%', (NEW.some_col[c]).a_text = 'VA';
END LOOP;
RETURN NEW;
END $BODY$;

CREATE TRIGGER trig_chk_mytab_input BEFORE INSERT OR UPDATE
ON mytable FOR EACH ROW
EXECUTE PROCEDURE chk_mytab_input();

and then when I insert some data with

INSERT INTO mytable VALUES (
DEFAULT,
'{
"(55, VA)",
"(1000, VA)"
}'
);

I get the following output (the two "RAISE INFO ..." statements):

INFO: t
INFO: f
INFO: t
INFO: f

but I expect all "t"s. So this means (I think) the VA in "(55, VA)"
statement is not the same with the VA in " RAISE INFO '%',
(NEW.some_col[c]).a_text = 'VA' " . But why?

Thanks in advance.