ASP.NET 4.0 Radio button checked changed event fires only once
<p>I have two radio buttons both set as async triggers for an update panel and problem is that first time one is clicked the CheckedChanged event fires but then no matter which radio button is clicked the event never fires again.</p>

<p>Markup:</p>

<pre><code>&lt;asp:RadioButton ID="rdoDeliveryBilling" runat="server" Checked="true" GroupName="DeliveryAddress" Text="Deliver to this address" AutoPostBack="true" OnCheckedChanged="rdoDelivery_CheckedChanged" /&gt;
&lt;asp:RadioButton ID="rdoDeliveryShipping" runat="server" GroupName="DeliveryAddress" Text="Deliver to a different address" AutoPostBack="true" OnCheckedChanged="rdoDelivery_CheckedChanged" /&gt;
&lt;asp:UpdatePanel ID="panDeliveryAddress" runat="server"&gt;
&lt;ContentTemplate&gt;
    ...delivery details form controls and validators goes here...
&lt;/ContentTemplate&gt;
&lt;Triggers&gt;
&lt;asp:AsyncPostBackTrigger ControlID="rdoDeliveryBilling" EventName="CheckedChanged" /&gt;
&lt;asp:AsyncPostBackTrigger ControlID="rdoDeliveryShipping" EventName="CheckedChanged" /&gt;
&lt;/Triggers&gt;
&lt;/asp:UpdatePanel&gt;
</code></pre>

<p>Code:</p>

<pre><code>protected void rdoDelivery_CheckedChanged(object sender, EventArgs e)
{
    ...only code that enables/disables the delivery form controls and validators goes here...
}
</code></pre>

<p>I have set a breakpoint inside rdoDelivery_CheckedChanged and it only hits the first time.</p>

<p>Any ideas?</p>
