I think mine moves when the upper and lower are seperate. Although when i installed my ambi safety I had to trouble at first like you are having. Just play around with it and maybe disassemble it it should be an easy fix.
The AR-15 safety should work whether it is assembled to the upper or not. It will NOT work if the hammer is not cocked. Repeat....the safety won't move to the "safe" position if the hammer is not cocked.