Steps to reproduce:
- In IE8 open url: http://www.zkoss.org/zksandbox/;
- Execute the code below;
- Expand nodes until a scrollbar will appear;
- Scroll down as shown at step1.png;
- Switch to tab2;
- Switch back to tab1;
Bug: The scroll bar is in initial state as shown at step2.png instead of being at the bottom.