That is odd. Currently Zumbie is not using epic's skeleton. We are going to be switching him over very soon (likely between 1.1 and 1.2) which should help with retargeting issues. Current zumbie isn't finished and we only included him for demo purposes. If your mesh is floating that is likely due a difference in root bones. When we move to the epic skeleton this issue should be fixed providing your mesh also uses epics skeleton.