[math-fun] Mma sum

How does one report bugs to Wolfram? In:=Sum[(-1)^k Binomial[m, k] k, {k, 0, m}] Out:=0 It gets the correct answer when m is given explicitly. I'm guessing it knows Sum[z^k Binomial[m, k] k, {k, 0, m}] and then chokes when it evaluates for z=-1. Veit