Yea I'm not sure, to be honest I have never had that issue either. Maybe try clearing SetCPU from SU permissions, then uninstall and re install it.
Okay so I think I may have figured it out. The problem was when I turned off my Xoom it would drop the mhz down to 216, but then would never go back to 1.5ghz. So I created a profile that told the max and min to be 1.5 when screen goes off. So far so good.