Seeing weird behavior with @ModelAttribute

[Rob Dennett]

I am using Spring 3.0.5 and I have a controller method similar to the following:

    @ModelAttribute("myFormBean")
    public MyFormBean getMyBean(HttpServletRequest request) {
        User user = Util.getUser;
        return new MobileInfoFormBean(user);
    }

    @RequestMapping(value = "/getAPage", method = RequestMethod.GET)
    public ModelAndView get(@ModelAttribute("myFormBean") MyFormBean bean, ModelAndView mav) throws ServiceNotAvailableException {
        if (bean.getProp().equals(Util.SOME_STATE)) {
            // do stuff
        }
        return mav;
    }

MyFormBean has two constructors, one of which is not intended to be called:

    public MyFormBean(User user) {
        //do stuff with user
    }


    // Adding zero-arg constructor to allow XML Marshalling
    public MyFormBean() {
        throw new NullPointerException("Must supply user when creating");
    }

This code is about two years old and has worked fine. Today, we were doing a deployment it was noticed that the no-arg version of MyFormBean was being invoked when going to /getAPage. Furthermore, we were unable to reproduce this problem in the QA environment or on my local Tomcat instance. All machines are running the same version of tomcat7 and are using the same JDK (1.7.0_51). The builds are made with the -source and -target flags set to 1.6 and with this release, we upgraded the production servers to 1.7.0_51.

Any ideas why this behavior might be happening?

Thanks,
Rob