ORDER BY with EXCEPT?

Howdy,

I was just updating a function in pgTAP that, given a schema name and  
an array of function names, returns a set of those function names that  
are not in the named schema. I got it working with a subquery, and  
David Fetter suggested that I try an EXCEPT query instead. The only  
problem is that it doesn't like my ORDER BY clause. The function is:

CREATE OR REPLACE FUNCTION  mytest(NAME, NAME[]) RETURNS setof text AS  
$$        SELECT quote_ident($2[i])          FROM generate_series(1, array_upper($2, 1)) AS s(i)        EXCEPT
SELECTquote_ident(p.proname)          FROM pg_catalog.pg_proc p          JOIN pg_catalog.pg_namespace n            ON
p.pronamespace= n.oid           AND quote_ident(n.nspname) = quote_ident($1)         ORDER BY s.i
 
$$ LANGUAGE SQL;

When I run this, PostgreSQL 8.3 tells me:

ERROR:  missing FROM-clause entry for table "s"
LINE 10:          ORDER BY s.i

Um, really" Have I not put the ORDER BY clause in the right place? Is  
this a bug?

Thanks,

David