So, let's check:
When you give the Goto-0 or Goto-Ref(erence) command with you receiver, does your motor end at exactly zero degrees?
If not, then with the buttons MoveEast/MoveWest move the motor to exactly zero degrees, and give a motor reset command. That should fix your motor zero again.
Let us know if this was the case, and worked?
Greetz,
A33