User blog comment:SirAston/URF and the LoL Engine - A To-Do List/@comment-24606304-20140402163324/@comment-24526576-20140402174527

Thats possible even in normal games. There is a difference between Amumu's Despair/Anivia's Ultimate and Swain's Ultimate. Because of the raising cost it is not possible in normal games to let it activated forever. Even not, if you're standing in base. Maybe that's the reason why it turns of after a while.