@JFreegman just taking a guess here but are you using a Radeon HD2000/3000/4000 series graphic card? In your case, it's indeed the GPU driver, Mesa sucks at blending, fglrx would work flawlessly but the latest fglrx which works with your card is too outdated for Xserver 1.12. (This is the same reason I am stuck on Kubuntu 12.04.1-.5 mixture.) 