Paint Weights tool subdivision surfaces

Why is it that after I paint weights to something, and I go back, the weights have re-assigned themselves on the joints. I go back fix it, and they mess up in a new way. I have this problem in the component editor, i can't set anything completely to zero, I change the value for one vertex and it re-assigns the rest to equal 1, it's so annoying. Why does it do this? I'm using maya 4

wrong forum

Sorry, I did that on accident, can an admin move it or something?