Bug with ORDER BY expression [ ASC | DESC ] ?

Hi, 
I am doing the following select in PostgreSQL 7.2.1 

select distinct on (o.sid,o.timepoint,o.lid,o.mid) o.sid,o.timepoint,o.lid,o.mid,o.value 
from onfvalue o, tempreftime t 
where o.sid=t.sid and o.timepoint=t.timepoint and o.lid=t.lid and o.mid=t.mid 
order by o.sid,o.timepoint,o.lid,o.mid,o.entrancetime desc;

but the result is coming in ascending order. 
There is no difference to 

select distinct on (o.sid,o.timepoint,o.lid,o.mid) o.sid,o.timepoint,o.lid,o.mid,o.value 
from onfvalue o, tempreftime t 
where o.sid=t.sid and o.timepoint=t.timepoint and o.lid=t.lid and o.mid=t.mid 
order by o.sid,o.timepoint,o.lid,o.mid,o.entrancetime asc; 

Is this a bug or am I missing something? 
Regards, Christoph