The popup of Chosenbox not updated after ZK-3986

Steps to Reproduce

http://zkfiddle.org/sample/vlqto9/1-ZK-3986

• click prepend than open the chosenbox
• click append than open the chosenbox

Current Result

The popup doesn't contain newly added items.

Expected Result

The popup should contain newly added items.

Debug Information

https://github.com/zkoss/zkcml/commit/e3e0de333d2a6a4b4c1b7b0db439ed44c11ac262#diff-fca8a08c8027cf2f92a1ecc3b1f0611aR853
If model.add(0, "item"), both index0 and index1 are 0.

After ZK-4446, the newly added item is visible now, but the position is wrong.

Workaround

Call invalidate() after model changed.