Minecraft crashes after Mojang logo on Mac when external monitor is connected

I attached a full system report in german and in English (sorry, translated it with Google translator)

What I expected to happen was...:
Minecraft showing me the home screen with multiplayer and options.

What actually happened was...:
Minecraft showed the Mojang logo an crashed afterwards. Displayed a crash report.

Steps to Reproduce:
1. Connect external monitor (I used a 24 inch one) via Thunderbolt/Display port
2. Close MacBook so external monitor becomes main display.
3. Start Minecraft an log in
4. When Mojang logo disapears, game should crash