Just updated Dark Sheep to the newest version 1.0.4.
Steam Overlay can rarely cause the game to crash, this seems to be a very rare and computer set-up specific issue. Most users didn't experience any crashes caused by the Steam Overlay and can use Steam Overlay normally.
Performed some code cleanups on my end, nothing that you'll notice during playing the game, but it did require me to push an update.
Enjoy the game!