When duplicating an action with the single-user button, the number between fake user and action name (for the sake of clarity) ), the new action is shown as having only a single user, despite the fact that the animation is applied to the armature/object and has a fake user. When the scene is saved and opened the action is lost (unless the action is actually assigned to an object). Prior to saving and loading, nothing can be done to increase the number of users in the action.