Do you have multiple monitors? That's been an issue for some people. It tries to fill the screen on boot. Although I've got two monitors and it only fills one of them. Not sure what causes it.
What graphics card do you have? And do you use any configuration stuff that combines your monitors into one?
Anyway if you check the config file you can change the "width" and "height" properties manually. Check the readme to find the config file: https://github.com/etodd/deceiver/blob/master/shipme.txt