calling codebehing page method won't timeout

I am calling a page method from javascript as shown below.  Sometime, the GetHotSellersAjax functions never completes but the timeout never occurs.  When I click a link on the page, or navigate away then I see the alert box from the timeout function.   Anyone know what I'm doing wrong?
 Thanks
 
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function pageLoad()
{
PageMethods.GetHotSellersAjax(onHotSalesLoaded, onTimeout, onError, null, 2);
}  function onHotSalesLoaded(result,userContext,methodName)
{

$get("lblBestSales").innerHTML = result;
}
function onTimeout(result)
{
alert("timeout loading hot seller");
} 
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