What I expected to happen...
When I opened the game through my snapshot profile I expected a normal splash screen.
What actually happened was...:
The window was the same old size but mostly black and down in the lower left hand corner was an itty bitty splash screen. Resizing the window did nothing. I tried clicking single player and it did nothing.
Steps to Reproduce:
Ok did I mention I'm using a Mac? I'm using a Macbook that runs on OS X 10.6.8. Also, when I switch back to my 1.6.2 profile I have no problem.

I just fire up the launcher, select my profile I use for snapshots and hit Play. The splash screen comes up and voila it has been shrunk.