IE9 only, tab will be hide after open then close

Click b then click a,
mousober on tabbox, tab "b" will be hide.
<zk>
<div height="300px" width="300px" style="border:1px solid black;">
<tabbox mold="accordion-lite" vflex="1">
<tabs>
<tab label="a"/>
<tab label="b"/>
</tabs>
<tabpanels>
<tabpanel style="overflow:auto">
<div height="290px" width="290px"/>
</tabpanel>
<tabpanel style="overflow:auto">
<div height="290px" width="290px"/>
</tabpanel>
</tabpanels>
</tabbox>
</div>
</zk>