Josh , if you have it set on one voice but it's doing a different voice i would 1. check and make sure that i actually have the right one checked .
2. if the right one is checked i would uncheck it and recheck it and exit from hal and restart hal and see if that fixes the problem , if it doesn't i am wondering if that agent program is causing problems ?
Also "if" the robotic sounding voice isn't one that needs to be used or you don't use it maybe you could delete it all together ?
Anyway this is what i would personally try , unless anyone knows any other better ways .