Paige and Phoebe gave Rick the face and body of Chris, and suddenly the Scabber Demons show up? First off, its been established in many seasons that demons track you by your powers. That was how it was with Cole, Whitelighters, and pretty much everyone else. So giving Rick Chris's face would mean absolutely nothing to the demons... unless they were sitting there watching the house for someone who looked like him to show up. But even then they would sense a lack of powers.