steps to reproduce

1. load the zul below

   <zk>
   	<zscript>
   		ListModelList myModel = new ListModelList(Locale.getAvailableLocales());
   		//hflex="min"
   	</zscript>
   		<bandbox>
   			<bandpopup >
   					<listbox id="mylistbox"
   						height="250px"
   						model="${myModel}" hflex="min">
   					</listbox>
   			</bandpopup>
   		</bandbox>
   </zk>
   

2. click to open the bandbox popup

actual result

the open popup has a horizontal scrollbar

expected result

the open popup can extend its width to eliminate the horizontal popup like ZK-2929