Using Javascript Confirm Dialog On A Button Within An UpdatePanel - Posting Back Full Page?

I basically want to show a dialog box with confirm or cancel options on it.

Confirm should allow the partial postback to take place, cancel should not. I have tried using a trigger and calling __doPostBack() as advised here but it posts back the full page not just the panel.

$('#buttonInUpdatePanel').live('click', function (event) {
event.preventDefault();
var item = this;
var title = 'Confirm';
var msg = 'Please confirm something';
var $dialog = $("<div id='myDialog'></div>")
.html(msg)
.dialog({
modal: true,
buttons: {
"Confirm": function () {
$(this).dialog("close");
__doPostBack('Button1', null); //tried this and .submit() on the button
//return true;
},
"Cancel": function () {
$(this).dialog("close");
//return false;
}
},
title: title
});
});

My UpdatePanel:

<asp:UpdatePanel ID="UpdatePanel2" UpdateMode="Conditional" runat="server">
<ContentTemplate>
<asp:TextBox runat="server" ID="TextBox1" />
<asp:Button
ID="Button1"
Text="Add"
OnClick="AddExtraVehicle_Click"
runat="server" />
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="Button1" EventName="Click" />
</Triggers>
</asp:UpdatePanel>

UPDATE:

I have changed the doPostBack to use the button ID now and commented out the return true and false lines. When I click the button it calls the confirmation dialog but when you click on confirm it appears to do nothing. I was expecting a call to the method AddExtraVehicle_Click but the breakpoint didn't trigger.