I just played a ranked solo q match (EUW) where our evelyn steals baron, but last hits it with a dot, AFTER going in to Mordekaiser ult. We all get the buff; increased AD/AP etc, but the buff doesnt empower minions. We try various lanes, we try returning to base in between our sieging attempts... Nothing works, the minions wont get empowered, and dies as fast as standard minions. Later during that game the enemy team kills baron, and the buff works properly.