Extremely slow order by queries

Hi, I have a scenario where data size is ~3M rows. My query is select C1, C2, C3 from T1 group by C1,C2,C3 This returns result in 30 Sec ( number of groups around 1 M ) While, if I modify the query to select C1, C2, C3 from T1 group by C1,C2,C3 Order by C1, C2 on the same dataset, it takes ~ 1 hour to get result. The platforms I tried is both widows 64 bit and Linux 64 bit, with latest monet installed. Both the machines have 4 cores. And the behavior is same on both the machines. I am really surprised to see overhead of second query. One more observation is that this query occupies only single core, while monet is free to utilize 4 cores. Regards, Manish