a4j:support not rerendering the radio buttons instantly

a4j:support not rerendering the radio buttons instantly

I have two radio sets and one is dependent on the other. I want to disable
the second one when there is a specified change in first one. I have used
a4j:support tag to accomplish it as shown in the code below
<td align="left">
<h:selectOneRadio value="#{wcbBean.wcbVO.IS_UNABLE_TO_PERFORM}">
<f:selectItem itemValue="1" itemLabel="Yes" />
<f:selectItem itemValue="0" itemLabel="No" />
<a4j:support event="onchange" action="#{wcbBean.setDegImpairState}"
reRender="rbDegImpair">
</a4j:support>
</h:selectOneRadio>
</td>
<td align="right">Degree of Impairment:</td>
<td align="left">
<h:selectOneRadio id="rbDegImpair"
value="#{wcbBean.wcbVO.DEGREE_OF_IMPAIRMENT}"
disabled="#{wcbBean.wcbVO.DISABLE_DEGREE_IMPAIR}">
<f:selectItem itemValue="TOTAL" itemLabel="TOTAL" />
<f:selectItem itemValue="PARTIAL" itemLabel="PARTIAL" />
</h:selectOneRadio>
</td>
The second set is not rendering again on changing the first set but after
a single click anywhere on the page. Why I need to click on the page to
disable the second set?