Question on "onLoading" with Ajax.request in Prototype

I'm using the following code attached.  Basically I want to have a standard loading animation until the content is pulled down from the server and inserted into the DIV element.  Now, using actual javascript (aka not the prototype framework) i have no problems.  But I'd like to use the framework across this site, but when i use the code below sometimes my output hangs on the loading image.  Often if i click the button that calls this function twice, it'll act normally.  If i remove the onLoading code, the program functions normally.  I've been scratching my head over this and am running out of time  as I've never really used the onLoading aspect of Ajax.request before.  Any help would be appreciated

function showWindow(id) {
	var url = id+".php";
	new Ajax.Request(url, {
	  method: 'get',
	  onSuccess: function(transport) {
		   $('searchresults').innerHTML = transport.responseText;
		},
		onLoading: function(transport) {
			$('searchresults').innerHTML = "Loading...<img style=\"vertical-align:middle;\"src=\"/img/loading.gif\"/>";
		}
	});
 
}

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