Ajax returned values do not update when field value changes
Check for any errors in Firebug's console. 
In Firebug's net tab, what is the value coming back from the XHR callback?


If the value coming back from the XHR is the old value, then your problem is on the server side. If the value coming back from the XHR is the new one, then your problem is on the client side (like JQuery not being able to find it's target element). Hope that helps.