it is your jQ selector 's problem.

Code:

var before=$('input');
console.log("before init:",before.length);
before.combobox({});

var after=$("input");
console.log("after init:"after.length);

//error!!!!
after.combobox("setValues", ['1','2','3']);

you will see in Console:

Code:

before init:1
after init:3

easyui generate other 2 input elements.

EasyUI object must be initialized before the method call