incorrect sort if using multiple keys with mixed order

hello t64-managers,

anyone knows if there is a bug on the sort command ?

DU 5.1A -

for eg. 
I want to sort data first by field 1 in ascending and then
by field 4 in numerically descending order.

but the command "sort -t'^' -k1 -k4nr <file>"  only gives
 the following output which is the same result as given
 by sort -k1 -k4n:-

q^d^D^20050623
q^e^D^20050626
q^f^D^20050628
x^c^D^20050609
x^e^D^20050611
x^h^D^20050616
x^k^D^20050621
y^a^D^20050619
y^b^D^20050621
y^c^D^20050622


Thanks for any response to my problem.

Frederick.
[email protected]