JavaServer Faces: ValueChangeListener doesn't write back to textfield

hello people,

i have an problem and as newbie of javaserver faces i couldn't solve this.

my jsf page have two textfields (textfield1 and textfield2) and i write a
new value at textfield1 and the valuechangelistner should calculate this and
write it back to textfield2. at moment the valuechangelistener works fine,
but i can't write the result of calculation in textfiled2

I couldn't find a similary problem at google. I get many results of
selectOneMenu, but nothing about my problem.

my JSP with JSF-Tags:

<h:inputText value="#{bean.textfield1}"
valueChangeListener="#{bean.textfield1Changed}"
onchange="this.form.submit()"
id="textfield1" converter="javax.faces.Float" size="80">

<h:inputText value="#{bean.textfield2}"
id="textfield2" converter="javax.faces.Float" size="80">

my javabean:
public void textfield1Changed( ValueChangeEvent event) {
    float newValue=((Float) event.getNewValue()).floatValue();
    // ... calculate newValue and output will back to textfield2

    //at this point i haven't an idea to write back
}

Have anyone a idea to resolve my problem.

thank you very much for an answer.

best regards
Michael Plate