Can you post the definition of your stored procedure? The test below was successful for me, though I used Sybase SQL Anywhere (I tried versions 12.0.1 and 11.0.1). The Sybase IQ server is based on the SQL Anywhere execution engine so this should be an equivalent test, though I'm unsure what version of SQL Anywhere corresponds to IQ 12.5.
create table mytable (column1 int, column2 int, column3 int);
create procedure myproc( parm varchar(10))
result ( column1 int, column2 int, column3 int)
begin
select 1,2,3;
end;
INSERT mytable (column1, column2, column3)
SELECT column1, column2, column3
FROM (myproc('AAA'));
Full disclosure: I work for Sybase in SQL Anywhere engineering.