Ah... so something has
changed....the Lab is now in at night. Even tho you say "they don't seem to mind each other", to me it's obvious Midnight is "mad" and he's not happy with that arrangement. Maybe he feels threatened, insecure being alone with the dog? Do you have a dog crate or kennel that you can put the Lab in at night? Or confine the kitten somewhere in a warm spot away from the Lab? Perhaps if you put Midnight away with Tigger, he would be happier. I've always kept my cats out of the bedroom at night, but that's my choice. Hope you can get Midnight straightened around again.