Spring MVC @ModelAttribute method not executed
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I have two portlets on the the same page (Liferay). Both controllers have symmetric methods and work on the same object (held in the session):

* `@ActionMapping` method which updates the object in the session
* `@ModelAttribute` method to get the object from the session and put it in the model
* `@RenderMapping` method which returns the JSP name to show the data of the object

Normally, after the action method is executed in one of the two portlets the other portlet is rendered again with the expected flow: `@ModelAttribute` method gets the changed object from the session and puts it in the model -> `@RenderMapping` -> JSP.

Sometimes though the `@ModelAttribute` method is not executed before the @RenderMapping method. This seems to be only the case when 

 1. action of portlet A is executed, both are rendered (all fine) 
 2. afterwards action of portlet B is executed (again user-triggered), A is rendered *without* executing the `@ModelAttribute` method

According to the [documentation][1]:

> @ModelAttribute methods in a controller are invoked before `@RequestMapping` methods, within the same controller
 
Why is this not working in this scenario? Are there any exceptions to the rule?

  [1]: http://static.springsource.org/spring/docs/3.1.0.RELEASE/reference/html/mvc.html#mvc-ann-modelattrib-methods