Error after changing URL pattern in web.xml

I have a simple vaadin6 application.  The servlet class is com.vaadin.terminal.gwt.server.ApplicationServlet.
When I had the following in web.xml, 
<servlet-mapping>
      <servlet-name>myservlet</servlet-name>
      <url-pattern>/*</url-pattern>
  </servlet-mapping>
and test in browser using http://localhost:8080/Vaad6Test-01/
everything works, the panel shows up.
I changed to:
<servlet-mapping>
      <servlet-name>myservlet</servlet-name>
      <url-pattern>/test1/*</url-pattern>
  </servlet-mapping>
and test in browser using http://localhost:8080/Vaad6Test-01/test1
I got the following error:
Failed to load the widgetset: /Vaad6Test-01/VAADIN/widgetsets/com.vaadin.terminal.gwt.DefaultWidgetSet/com.vaadin.terminal.gwt.DefaultWidgetSet.nocache.js?1446873500415

Why can't I change the url pattern?

Found the answer here:
https://vaadin.com/forum#!/thread/136600