PopulateInitialSubscriptions callback is not being invoked after getting Realm instance

I am having an issue where PopulateInitialSubscriptions is not being called when running my mobile application. As i understand it, it is only ran once for the lifetime of the realm. Is this true? The reason for the question is because I added a new initial subscription but it is not being added because the callback is never invoked. Is there a way to manually invoke the callback so that anytime I add a new subscription, it will be added to the initial subscription list?