disable or enable a inputTextarea in primefaces fail for second time

Question

I´m trying to enable or disable a inputTextarea by select a option in selectOneMenu.

If there is no value select it will be disable but if one value is select, will be enabled.

My problem is, I select a option and enable, i select no option and disable, and stop to refresh the component.

                <p:row>
                    <p:column>
                        <p:outputLabel value="#{lbl['LABEL.ALTERARPARA']}"/>
                    </p:column>

                    <p:column>
                        <p:selectOneMenu value="#{atendenteBean.statusAlterado}" label="#{lbl['LABEL.ALTERARPARA']}" converter="atendenteStatusConverter" filter="true" filterMatchMode="contains">
                            <f:selectItem itemLabel="" itemValue="#{null}"/>
                            <f:selectItems value="#{atendenteBean.statusPossiveis}" var="status" itemLabel="#{status.descricao}"/>
                            <p:ajax update="motivo" event="change"/>
                        </p:selectOneMenu>
                    </p:column>
                </p:row>

                <p:row>
                    <p:column>
                        <p:outputLabel value="#{lbl['LABEL.MOTIVO']}"/>
                    </p:column>

                    <p:column>
                        <p:inputTextarea id="motivo" value="#{atendenteBean.pojo.motivo}" maxlength="100" cols="100" disabled="#{empty atendenteBean.statusAlterado}"/>
                    </p:column>
                </p:row>