bandbox - messed display after its style changed

<vbox>
<bandbox id="test" width="200px" buttonVisible="false"/>
<button label="test" onClick="doClick()"/>
<zscript>
void doClick()

{ test.setButtonVisible(true); test.setStyle("background-color:yellow;"); }

</zscript>
</vbox>

if the test button is clicked then display bandbox becomes chaotic