I just noticed that when I publish an action on the user's timeline for the same object multiple times, using facebook's 'built-in' action type (eg: 'read' an article), i get an error response, something like "action is already associated to the user on this object". But when i try to do the same for a custom action that i created(eg: 'agreed' with an article), I don't get any error message, instead the actions gets published multiple times. I want my custom action to behave just like facebook's default action-type.