Vaadin Servlet and Session is not loaded correct in 7.5.2

I use a UI(WX) to redirect the application to UI_TK(${URI}/TK?agent=${agent.id}) and UI_Reg(${URI}/Reg?code=${code}) based on some incoming parameters.

class WX extends UI {

    @Override
    protected void init(VaadinRequest request) {
        ......
        if(currentUser.isAuthenticated()){
......
           getPage().setLocation("${URI}/TK?agent=${agent.id}")
        }else{
......
            getPage().setLocation("${URI}/Reg?code=${code}")
        }
......
    }
}

The servlet code is here:

class IncanaServlet extends TouchKitServlet {
    
    Log log = LogFactory.getLog(this.class)

    @Override
    protected void servletInitialized() throws ServletException {
        super.servletInitialized()
        
        getService().addSessionInitListener(new SessionInitListener() {
                    @Override
                    public void sessionInit(SessionInitEvent event) {
                        event.getSession().addBootstrapListener(new BootstrapListener(){
                                    @Override
                                    public void modifyBootstrapPage(BootstrapPageResponse response) {
                                        ......//Generate some element to add to body
                                        VaadinRequest vr = getService().getCurrentRequest()
                                        String URL = vr.getRequestURL().toString()
                                        //URI will be TK for register and Product for buying
                                        String URI = vr.getRequestURI()
                                        String query = vr.getQueryString()
                                        ........//Generate some element to add to body
                                        body.append(......)//Add the html element
                                    }

                                    @Override
                                    public void modifyBootstrapFragment(BootstrapFragmentResponse response) {
                                    }
                                })
                    }
                })
    }

When in Vaadin 7.4.7

The log shows the sessionInit is called after getPage().setLocation("${URI}/TK?agent=${agent.id}") and before the UI_TK is loaded.

• load UI_WX
• load SessionInitListener(vr.getQueryString() is right)
• load UI_TK

When in Vaadin 7.5.2

The log shows the sessionInit will be called 2 or 3 seconds later after getPage().setLocation("${URI}/TK?agent=${agent.id}") and after the UI_TK is loaded.

• load UI_WX
• load UI_TK
• (2 or 3 seconds later)load SessionInitListener(vr.getQueryString() is empty)

Which means the SessionInitListener can not get the real QueryString(): String query = vr.getQueryString()

I try several times and I think the only reason is the version of Vaadin!