unable to update a single valued autocomplete lookup field


I have deployed this great Autocomplete lookup field, inside my team site but i am facing this problem only when i leave "Allow multiple values" check box un-checked. the scenario for re-producing the problem is as follow:-
  1. I have a list which contain an Autocomplete lookup field named "Area", which does not allow multiple values.
  2. Now inside my list I add a new item, and i enter a value inside the Autocomplete lookup column "Area", and i saved the new item and everything went well.
  3. then i edited the item and i remove the current value for the Area, and i add a new value for the Area, then i save my modification.
  4. but the problem is that the lookup field will be empty.
now if i edit the item again and i add a new value for the Area it will be saved, also if i allow "multiple selection" for the autocomplete look-up column it will work well from the begening.

so seems the problem is related to the following 2 facts:-
  • if i uncheck the "allow multiple values" inside the lookup field.
  • Then i can only update the lookup field value, incase it does not have any value. while if it has a value and i remove it then add a new value, in this case the new value will not be saved, and the autocomplete lookup field will be empty.
Can anyone adivce on this please?