"First Project" Movement Issue

I copied and pasted the example from First Project but the forwards and backwards movement (KEY_W, KEY_S) is all slanted. It strafes left and right just fine but forwards and backwards move on a slant. The kicker is, if I define __DEBUG__ and have it run in a window (instead of full screen), everything works fine.

For new users (like myself) this is very confusing behaviour. Just wanted to alert someone that the primary example most people will see first has this bug.