org.zkoss.zkmax.zk.ui.util.DesktopRecycle does not work

...
	<listener>
		<description>DesktopRecycle-Listener</description>
		<listener-class>com.spp.config.MyRecycle</listener-class>
	</listener>
		
</zk>

package com.spp.config;
import org.zkoss.zk.ui.Desktop;
public class MyRecycle extends org.zkoss.zkmax.ui.util.DesktopRecycle {
  protected boolean shallCache(Desktop desktop, String path, int cause) {
	  System.out.println("Shall cache? " + desktop +", "+path+", cause: "  + cause);
    return true;
  }
  protected boolean shallReuse(Desktop desktop, String path, int secElapsed) {
	  System.out.println("Shall reuse? " + desktop +", "+path+", secs: "  + secElapsed);
    return true;
  }
}