ASP.NET MVC 2.0 Ajax call - LoadingElementId not re-hidden when OnSuccess script specified

I'm writing a very simple web application in ASP.NET MVC 2.0 which is used as a test interface for a web service. The various pages present a user interface to input the parameters for the request messages. The parameters are submitted back to the controller via Ajax, which returns a partial view containing the response SOAP message (HTML encoded XML) in a <pre> tag...

// In controller...
ActionResult WebMethodTest()
{
    return View(new WebMethodModel());
}

[HttpPost]
ActionResult WebMethodTest(WebMethodModel model)
{
    model.Response = MyServiceProxy.WebMethod(model.Request);
    return PartialView("SoapResponse", model.Response);
}

// In view
<% using (Ajax.BeginForm(new AjaxOptions { UpdateTargetId="Response", LoadingElementId="Loading", HttpMethod="POST", OnSuccess="prettyPrint"}))
   { %>
    <!-- various model bound controls... -->
<% { %>

<div id="Loading" style="text-align:center; display:none">
    <img src="../../Content/ajax-loader.gif" alt="loading..." /><br />
    working...
</div>

Unfortunately the Loading div element is not being hidden again when the data is returned after the Ajax call, it stays visible. Interestingly, it does get hidden correctly if I remove OnSuccess="prettyPrint". I get the impression that my OnSuccess script is overriding the default behaviour, rather than executing in addition. I don't want to lose prettyPrint though as it's colourizing the XML which is being displayed... how can I keep the default loading element behaviour as well as my own O开发者_开发技巧nSuccess hook?

Cheers!

I resolved this issue by amending the OnSuccess script to this:

OnSuccess = "function() { prettyPrint(); return true; }"

So it seems that, like OnBegin, returning false (or anything other than true) cancels the operation, although by this stage the DOM has already been updated, so the only thing you can canel is hiding the Loading element... which doesn't seem terribly useful!