Inconsistent stair transformation when placed next to other stairs

When stairs are placed next to other stairs in certain configurations, they sometimes change into corner stairs and sometimes do not. Does not appear to be related to direction.

See the attached images. In both images I've placed a ring of stairs, and subsequently placed three stair blocks along the side(s) of that ring. The outer 2 of these 3 final stair blocks inconsistently change to corner stairs, as shown. I should note that when placing these final stairs I was facing a consistent direction and angle and was aiming at the ground when placing them.

Also, while different coordinates result in different results, removing and replacing a stair always seems to yield the same result (unless changing the direction/angle you're facing), almost as if each coordinate has a predetermined result.

Possibly related to MC-12642.