Green's Theorem Proof Misunderstanding

By the way, I also posted this in the Urgent Help section.

Okay, I get the half that is normally explained in the books which is the same as on wikipedia (http://en.wikipedia.org/wiki/Green's_theorem).

This is the best that I can explain this:

I understand the part of the explaination where *integral of (P dx) = - double integral of (partial derivative of P with respect to y) dA*.

I don't, however, understand why on the other half, *integral of (Q dy) = double integral of (partial derivative of Q with respect to x) dA*, does not have a negative sign in front of one of the two halves.

If essetially you are doing the same process twice, once with a type I region and the other time with a type II region, why does one half of the proof end up with a negative (which I understand) but not the other half?