> Can you explain why is a necessity to accept that people do
> things against documentation and write stored procedure with RETURNS
> clauses but without SUSPEND statements?

because PSQL compiler does not complain when it sees following code:

CREATE PROCEDURE test(a INTEGER) RETURNS (b INTEGER)
AS BEGIN
b = a;
END

Since compiler does not complain, this procedure is fully legitimate.
But when I check whether it has output params and use "SELECT * FROM
test(1)" I get empty result set, not a result set with 1 row and 1 column.