Steps to Reproduce

1. run attached zul
2. select an item in combobox
3. click to expand the dropdown

Actual:

scrollbar moves to the right automatically:

every time you click combobox to expand the dropdown, the scrollbar scrolls to the right.

Expected:

scrollbar remains being on leftmost position.

Extra Information

It might relate to ZK-2193.

I have tested 6.5.6.FL.20140430, and it also has this issue.