Enabling json calbacks in Alfresco 4.0
Just placing a customized copy in shared/classes/alfresco does not work as beans still resolve from alfresco/WEB-INFO/classes/alfresco.
Try putting your customizations in shared/classes/alfresco/extension/whatever-context.xml.
The order of the imports is defined in alfresco/WEB-INF/classes/alfresco/application-context.xml - the last definition overrides and "wins".