Differentiation of the summation?



Hello all,

I have tried to do differentiation of the summation by indexed variables:

(C1) diff( sum(Y*X[i],i,0,n), Y);
(D1) 'SUM(X[i],i,0,n)

(C2) diff( sum(Y*X[i],i,0,n), X[i]);
(D2) 'DIFF('SUM(X[i],i,0,n),X[i],1)*Y

For C1 everything is OK, but I have expected as a result of C2  a constant 
value Y for 0<=i<=n. 

Is it possible to do such type of differentiation in Maxima or not?
If it's possible, how can I perform this operation in Maxima?

Thanks in advance.

-- 
Miha Krasnik