weird startup screen when starting up with a unique resolution

Put the summary of the bug you're having here

What I expected to happen was...:
Minecraft should open with a neat new title screen

What actually happened was...:
It was blurred and weird

Steps to Reproduce:
1. Change Resolution to 1280x600 in the minecraft launcher
2. start up the prerelease(you need to wait for a bit to let this happen)
3.It shows a weird and can see nothing(buttons still works)