Please try to add a 'focus' event to the inputing box.
$.extend($.fn.combobox.defaults.inputEvents, {
focus: function(e){
var target = this;
var len = $(target).val().length;
setTimeout(function(){
if (target.setSelectionRange){
target.setSelectionRange(0, len);
} else if (target.createTextRange){
var range = target.createTextRange();
range.collapse();
range.moveEnd('character', len);
range.moveStart('character', 0);
range.select();
}
},0);
}
})