There is a bug in wiquery-autocomplete.js where JS gets options parameter from JQuery UI autocomplete and always treats it as an array - however, for AJAX-filled autocompletes this is a string, resulting in JS error.
I have created a Wicket quickstart project demonstrating the bug, with detailed instructions how to trigger it on the start page, download here: http://lemming.hofyland.cz/wiQueryAutocompleteJSBug.zip