My guess is that when an 'experience award event' occurs, a check is made against the player's current experience/AA levels. If at 99.99% or 230AA (for lvl 115s) the experience that would have been awarded is completely discarded. It "poofs". It's part of a fundamental system, and should not be altered. Fellowship is an add on, downstream from this fundamental system. Therefore, the cup can never runneth over.