I use a AjaxTabbedPanel on my page and run into the following problem:
If there is an Behavior (AjaxSelfUpdatingTimer or AbstractAjaxTimerBehavior) attached to one of the panels and the panel is replaced by another panel, the AjaxBehavior is not properly removed and deactivated. After the idle-duration the JS calls in and Wicket throws an exception due to the missing behavior.
ERROR - DefaultExceptionMapper - Unexpected error occurred
org.apache.wicket.behavior.InvalidBehaviorIdException: Cannot find behavior with id '0' on component 'org.apache.wicket.markup.html.panel.EmptyPanel:tabs:panel' in page '[Page class = com.wicket.HomePage, id = 0, render count = 4]'. Perhaps the behavior did not properly implement getStatelessHint() and returned 'true' to indicate that it is stateless instead of returning 'false' to indicate that it is stateful.
I attached a quickstart showing the problem. Simply take a look at second tab and then go back to the first tab and you run into this problem.
There is a workaround for this: If you attach the behavior to a component of the panel (i.e. the clock) this error doesn't occur.