All I can think of us is that the cold has thrown their (her) system off. Just like any other stresser...extreme heat, moving, adding new flock-mates, egg laying, including the egg cycle, can be thrown out of whack. Of course there could be a physical issue, but I don't have a clue what it could be, as I've not heard of "accidental" egg laying overnight with perfectly good eggs, only the malformed "oops" eggs. I'd give it a week or so (although I'm sure the waste of eggs
) to see if it works it way out. In MY case, I'd add a bit of heat on really cold nights (assuming stress), but many frown on that
I sure hope it works itself out for you soon though; with three molters I'm getting very few eggs.
Oh, and I don't know how long your roost is, but maybe you can toss several handfuls of bedding on the dropping board along the line of where you're finding the broken eggs. That way you're still getting the benefit of a dropping board, but it'll soften the landing of an egg just enough to keep it from cracking if another accident happens. I always toss a little bit of bedding up there anyway to help absorb watery droppings...