When I entered the "Find the Acorn" or "Buzz and Violet" contest, it says that I've already entered this month. I think it's a mistake, so what's wrong?

This message appears when folks want to be sure they entered the contest. They hit "submit" and press hard on the mouse or "return" key. It is recorded instantly but when the mouse button is held down longer than it needs to be, it thinks you're attempting to submit a second entry.