splitter of borderLayout problem

In IE6;
1. Click collapse button of right splitter.
2. The splitter will move to the end of right side.
3. Drag left splitter to the end of right side.
4. Click collapse button of right splitter.
5. Right splitter will move to the left side and excess the Left splitter.

<zk>
<borderlayout height="500px">
<center border="0">
<borderlayout>
<west maxsize="600" minsize="300" size="30%" flex="true" border="0" splittable="true">
<div style="background:#E6D92C">
<label value="30%"
style="color:white;font-size:50px" />
</div>
</west>
<center>
<label value="Here is a border"
style="color:gray;font-size:30px" />
</center>
<east size="30%" flex="true" border="0" collapsible="true">
<div style="background:#B8D335">
<label value="30%"
style="color:white;font-size:50px" />
</div>
</east>
</borderlayout>
</center>
</borderlayout>
</zk>