Bug with ordering aggregates?

Greetings,
 This doesn't seem right to me:

postgres=# select
postgres-# string_agg(column1::text order by column1 asc,',')
postgres-# from (values (3),(4),(1),(2)) a;string_agg
------------1234
(1 row)
 I'm thinking we should toss a syntax error here and force the 'order by' to be at the end of any arguments to the
aggregate.Alternatively, we should actually make this work like this one does: 

postgres=# select
postgres-# string_agg(column1::text,',' order by column1 asc)
postgres-# from (values (3),(4),(1),(2)) a;string_agg
------------1,2,3,4
(1 row)
Thanks,
    Stephen