ListModelList clear cause listbox to not add new listitems

Steps to Reproduce

https://zkfiddle.org/sample/2crdgfr/2-Another-new-ZK-fiddle

Open drop down, select an value

Current Result

Drop down is empty after update

Expected Result

Drop down contains "beep" "bop" after update 

Debug Information

Seem to happen after:

https://github.com/zkoss/zk/commit/af6698a368b236824b70da2e6c237d9932378361#diff-45450f3948e27c39e03b7c9692a231a21a7c9397ad15faf3f10858bb7d337497R188

Workaround

create a new ListModelList instead of using clear(), and use notifyChange to replace the listmodel in the view.