Strange ValueChangeListener effect

[[EMAIL PROTECTED]]

If I select the item of the fist listbox both ValueChangeListeners 
are called. If I select the item in the second listbox only the 
ValueChangeListener of the first listbox is called. If I select a 
second time the item in the second listbox no valueChangeListener is 
called.
What can I do to fix this effect?



  <h:selectManyListbox value="#{sell.assortments}" size="6" 
onchange="this.form.submit()"
                                valueChangeListener="#{sell.assortmentChange}"> 
      <f:selectItems value="#{sell.assortmentChoice}" /> 
    </h:selectManyListbox> 

  <h:selectManyListbox value="#{sell.categories}" size="6" 
onchange="this.form.submit()"
                                valueChangeListener="#{sell.categoryChange}"> 
      <f:selectItems value="#{sell.categoryChoice}" /> 
    </h:selectManyListbox>