Understanding WebFlow on Grails

I'm using Spring Web Flow on Grails (2.0.8.1 on grails 2.3.11). I've created all dir under views and this is my little flow:

    def registrazioneUtenteFlow = {

        log.info("Registrazione Flow")

        step1_informazioni_personali {
            on("next").to("step2_informazioni_personali")
        }

        step2_informazioni_personali {
            on("submit").to "step3_informazioni_personali"
            on("return").to "step1_informazioni_personali"
        }

        step3_informazioni_personali {

        }
    }

I created three gsp under controllerName/flowName. Inside each JSP there is a form with a submit button. Ex. for first GSP:

<g:form action="registrazioneUtente">
     <g:submitButton name="next" value="NEXT" />
</g:form>

Now.. If i put inside the state the "on" rule, I have an 404 with this url

registrazioneUtente?execution=e8s1&format=

But if I leave this from step1_informazioni_personali, I can see the page.

Why?!?

Thanks in advance