Minecraft PE starts fine, asks for XBox Live credentials the first time (As expected) and logs you into Xbox Live.
In the lower left the icon changes to a chat icon with a person and text bubble. If you click this bubble - Minecraft PE crashes.
If you log out of Xbox Live, this icon changes back to allow you to click it and login to Xbox Live. Once logged in and the icon returns to dude with chat window...clicking that button crashes Minecraft.