Listbox size change when click the listitem

As the follow code:
<zk>
<div>Scroll to the right. You should NOT see the last 2 Columns.</div>
<listbox width="400px">
<listhead>
<listheader label="Column 1" width="250px" />
<listheader label="Column 2" width="250px" />
<listheader label="Column 3" hflex="2" />
<listheader label="Column 4" hflex="1" />
</listhead>
<listitem forEach="1,2,3">
<listcell forEach="1,2,3,4">Listcell</listcell>
</listitem>
</listbox>
</zk>

When use IE9(IE10 ok), connect the zul. the listbox size change when click the list item. The issue happen after 7.0.2, before 6.5.x is normal.