Hi I got a problem with change event. By documntation there should be object ui.item
After an item was selected; ui.item refers to the selected item.
if ui.item is not defined that means your json source is not well formed. You have to send a json source like this:
[{"label":"Jean","value":1},{"label":"carl","value":2}]
You can add more key to the array but at least you have to set "label" and "value". Check the json string. Also I reckon you to use the last version of autocomplete 1.8.1 at the moment