Edit: Changing report to accurately reflect what happened

https://www.youtube.com/watch?v=6hSeplVVf8g

Cats path-finding is attracted to sit on the upside down stairs as shown in the video. When they are on it, they can't breed. When they are moved with a water bucket or teleported away when the player has moved far enough and they aren't standing on the block, they do breed. There is no furnace (or anything upstairs), or anything else nearby that would cause the cats to want to go to that block specifically.