Client not showing up / freezing after champ select

While trying out various masterys on different champions I tried to play Darius in customs with the deathfire mastery on. After picking him, either the game would freeze up as I picked him (with the sound and music still in the background) or the client would close itself to start up the game. The game would never start, and not only that, my computer would freeze and become inresponsive. This only seems to happen with picking Darius as I have been able to pick Yorick and Twitch with no problems.To recreate it, just take deathfire on Darius and go into a custom game.