This is a repeat MC-147868, which addresses the same issue, however it seems as if that page was longer being updated, and was not being given the attention that the bug deserves.

This is an issue in which the stairs leading up to some of the buildings in the snowy tundra were not generating with the appropriate properties. Specifically, two of the stair blocks would not generate as corner stairs even though they should in the given context.

To reproduce, simply go to any snowy tundra village and you will almost certainly find a building with this bug.