I'm getting half the hashrate issue with cgminer 3.3.1 on Windows (downloaded from the official place earlier this evening). Maybe it's just a cgminer issue rather than your build?
Now that's rather odd. You'd think given Windows's prevalence that folks would be discussing it already, but maybe very few have two USB miners plugged into the same computer. Fortunately, I've been able to plug one into the laptop at home and one into the laptop at work, so I'm covered.
Edited to add: Still, each hardware device is reporting roughly half speed to the pool, even from separate computers. Sorry for the confusion!