select random order by random

Dear sirs,

I was very surprised when I executed such SQL query (under PostgreSQL 8.2):
select random() from generate_series(1, 10) order by random();

I thought I would receive ten random numbers in random order. But I received
ten random numbers sorted numerically:
      random
-------------------
 0.102324520237744
  0.17704638838768
 0.533014383167028
  0.60182224214077
 0.644065519794822
 0.750732169486582
 0.821376844774932
  0.88221683120355
 0.889879426918924
 0.924697323236614
(10 rows)

I don't understand - why the result is like that? It seems like in each row
both random()s were giving the same result. Why is it like that? What caused
it?

--
Piotr Sobolewski
http://www.piotrsobolewski.w.pl