java.util.ConcurrentModificationException

Anybody seen this before?

java.util.ConcurrentModificationException
   at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
   at java.util.HashMap$KeyIterator.next(HashMap.java:828)
   at com.vaadin.terminal.gwt.server.JsonPaintTarget.addAttribute(JsonPaintTarget.java:454)
   at com.vaadin.ui.AbstractOrderedLayout.paintContent(AbstractOrderedLayout.java:192)
   at com.vaadin.ui.AbstractComponent.paint(AbstractComponent.java:781)
   at com.vaadin.ui.TabSheet.paintContent(TabSheet.java:435)
   at com.vaadin.ui.AbstractComponent.paint(AbstractComponent.java:781)
   at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.writeUidlResponce(AbstractCommunicationManager.java:1040)
   at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.paintAfterVariableChanges(AbstractCommunicationManager.java:927)
   at com.vaadin.terminal.gwt.server.AbstractCommunicationManager.doHandleUidlRequest(AbstractCommunicationManager.java:794)
   at com.vaadin.terminal.gwt.server.CommunicationManager.handleUidlRequest(CommunicationManager.java:296)
   at com.vaadin.terminal.gwt.server.AbstractApplicationServlet.service(AbstractApplicationServlet.java:501)

Douglas W Ferguson: Anybody seen this before?

Yes, many times.

If it only happens some times, it's probably the same as e.g. this forum post.

If it happens every time, it might be a bug in Vaadin. In that case, please file a bug at http://dev.vaadin.com with instructions on how to reproduce the issue.