steps to reproduce

1. run zssapp
2. open demo_sample.xlsx
3. move the chart several times

current result

Exception in thread "Thread-8" java.lang.IllegalStateException: Before calling Executions.activate(), the server push must be enabled for [Desktop z_msi:/WEB-INF/index.zul]
at org.zkoss.zk.ui.impl.DesktopImpl.checkSeverPush(DesktopImpl.java:1499)
at org.zkoss.zk.ui.impl.DesktopImpl.activateServerPush(DesktopImpl.java:1505)
at org.zkoss.zk.ui.Executions.activate(Executions.java:1000)
at org.zkoss.zk.ui.Executions.activate(Executions.java:972)
at org.zkoss.zss.app.ui.AppCtrl$19$1.run(AppCtrl.java:774)
at java.lang.Thread.run(Thread.java:745)