The "accept" attribute of Button used to upload doesn't work for multiple file type

Problem Description

A forum user reported http://forum.zkoss.org/question/94362/upload-attribute-accept-multiple-file-extensions/

The syntax for "accept" attribute is described in http://books.zkoss.org/wiki/ZK_Component_Reference/Essential_Components/Button#Upload

Steps to Reproduce

1. run the zul below

      <zscript><![CDATA[
   	import org.zkoss.util.media.Media;;
     	public void myProcessUpload(UploadEvent event){
     		System.out.println("uploaded");
     		Media media = event.getMedia();
     		System.out.println("uploaded "+media.getName()+", size:"+(media.getByteData().length/1024)+" k bytes");
     	}
     ]]>
     </zscript>
   <button label="file extension" upload="true,maxsize=-1,accept=.png|.pdf" onUpload="myProcessUpload(event)"/>
   

2. click the button

Actual Result

popup dialog cannot display png and pdf file

Expected Result

filter both png and pdf files