SQL_ERROR_LOG plugin doesn't log errors produced with SIGNAL

Since SQL_ERROR_LOG logs all errors that happen withing a stored procedure (while only the last one is returned to the user), it can be a useful debug tool. Thus I've tried to use SIGNAL to add debug messages to my procedures during development, but it seems that the SIGNALed errors are not logged:

DELIMITER ||

DROP PROCEDURE IF EXISTS t;

CREATE PROCEDURE t()

BEGIN

	DECLARE n TINYINT UNSIGNED DEFAULT rand();

	DECLARE CONTINUE HANDLER

		FOR SQLSTATE '01000'

		DO NULL;

	IF n <= 1 THEN

		SET @dbug_msg = CONCAT('n=', n);

		SIGNAL SQLSTATE '01000' SET

			MYSQL_ERRNO = 1644,

			MESSAGE_TEXT = @dbug_msg;

	ELSE

		SIGNAL SQLSTATE '01000' SET

			MYSQL_ERRNO = 1644,

			MESSAGE_TEXT = 'Hey... how did this happen??';

	END IF;

	DO 'something';

END;

||

DELIMITER ;

CALL t();

If you replace SIGNAL with SELECT 1 FROM not_existing_table, the error is logged (DECLARE HANDLER doesn't interfer with SQL_ERRORS_LOG, and this is good).

I used '01000' SQL STATE and 1644 code because they are not warnings.