Crashes on MAC when loading.

Minecraft crashes when loading up after clicking play on the new launcher.

I thought that the game was going to open up onto the Mojang title screen shown when loading the main menu of Minecraft.

The Minecraft window opened up (after clicking play) stays there for about 1 second then vanishes and the new launcher shows the crash report.

Steps to Reproduce:
1. Open up the MinecraftDev for snapshot 13w19a.
2. Log in (if not logged in already).
3. Click play.