On a Mac, when I set "Don't Starve" to Fullscreen, then start the game fresh, the screen is shifted up off the screen by about the same distance as the height of the application dock. I have to go to settings again, turn off fullscreen, then turn it back on for it to shift back down where it belongs.
Mac Pro Desktop
1. Start, "Don't Starve" 2. Click, "Options" 3. Enable, "Fullscreen" 4. Exit, "Don't Starve" 5. Start, "Don't Starve" 6. The screen will be shifted up.