@smitchell I don't think it's an integer issue 'cause the creator (spawner) sprite isn't place on float position.
My best guess it that sometimes, the collision isn't triggered. And if you miss even just once, no background will be created anymore so... white screen.
So I think you shouldn't use sprite to check for position but just position check it's more reliable.
like that scrollingBullet.capx
Also, using bullet behavior to scroll a background is interesting, never thought about that.