we using your pivottable-demo 2.0.1 without change any source.
http://localhost:8080/pivottable-demo/airline.zul

Fistly, drag "Customer", "Flight", "Date" from unused area to values area,
when dragging "Customer" back to unused area, error occured.

2013-1-24 16:35:40 org.zkoss.zk.ui.impl.UiEngineImpl handleError:1281
严重: >>java.lang.ArrayIndexOutOfBoundsException: 3
>> at org.zkoss.pivot.impl.TabularPivotModel.getCalculator(TabularPivotModel.java:451)
>> at org.zkoss.pivot.impl.TabularPivotModel.getValue(TabularPivotModel.java:434)
>> at org.zkoss.pivot.impl.util.DataCellTraverser$SingleCellFillCtx.fill(DataCellTraverser.java:203)
>> at org.zkoss.pivot.impl.util.DataCellTraverser$SingleCellFillCtx.fill(DataCellTraverser.java:180)
>> at org.zkoss.pivot.impl.util.DataCellTraverser$SingleCellFillCtx.fill(DataCellTraverser.java:175)
>> at org.zkoss.pivot.impl.util.DataCellTraverser$SingleCellFillCtx.fill(DataCellTraverser.java:162)
>> at org.zkoss.pivot.impl.util.DataCellTraverser$SingleCellFillCtx.access$400(DataCellTraverser.java:139)
>> at org.zkoss.pivot.impl.util.DataCellTraverser.fill(DataCellTraverser.java:134)
>> at org.zkoss.pivot.impl.util.DataCellTraverser$1$1.onNode(DataCellTraverser.java:125)
>> at org.zkoss.pivot.util.Trees.traverse(Trees.java:232)
>> at org.zkoss.pivot.util.Trees.traverse(Trees.java:193)
>> at org.zkoss.pivot.util.Trees.traverse(Trees.java:180)
>> at org.zkoss.pivot.impl.util.DataCellTraverser$1.onNode(DataCellTraverser.java:119)
>> at org.zkoss.pivot.util.Trees.traverse(Trees.java:232)
>> at org.zkoss.pivot.util.Trees.traverse(Trees.java:193)
>> at org.zkoss.pivot.impl.util.DataCellTraverser.fill(DataCellTraverser.java:100)
>> at org.zkoss.pivot.Pivottable.onInitRender(Pivottable.java:589)
>> at sun.reflect.GeneratedMethodAccessor65.invoke(Unknown Source)
>> at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
>> at java.lang.reflect.Method.invoke(Method.java:597)
>> at org.zkoss.zk.ui.impl.EventProcessor.process0(EventProcessor.java:207)
>> at org.zkoss.zk.ui.impl.EventProcessor.process(EventProcessor.java:138)
>> at org.zkoss.zk.ui.impl.UiEngineImpl.processEvent(UiEngineImpl.java:1626)
>> at org.zkoss.zk.ui.impl.UiEngineImpl.process(UiEngineImpl.java:1410)
>> at org.zkoss.zk.ui.impl.UiEngineImpl.execUpdate(UiEngineImpl.java:1134)
>> at org.zkoss.zk.au.http.DHtmlUpdateServlet.process(DHtmlUpdateServlet.java:562)
>> at org.zkoss.zk.au.http.DHtmlUpdateServlet.doGet(DHtmlUpdateServlet.java:457)
>> at org.zkoss.zk.au.http.DHtmlUpdateServlet.doPost(DHtmlUpdateServlet.java:465)
>> at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
>> at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
>> at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
>> at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
>> at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
>> at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174)
>> at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
>> at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
>> at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
>> at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
>> at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:874)
>> at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
>> at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
>> at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
>> at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
>> at java.lang.Thread.run(Thread.java:619)