The Bug:

Stairs occasionally have incorrect block states after upgrading old worlds.

Steps to Reproduce:

• Launch an instance of 1.11.2.
• Build the setup as shown in the attachment below. setup.png
• Exit the world and upgrade it into the latest snapshot.
• Look at the block states of the stairs closely.
• Take note as to whether or not stairs occasionally have incorrect block states after upgrading old worlds.

Observed Behavior:

Stairs occasionally have incorrect block states after upgrading old worlds.

Expected Behavior:

Stairs would retain their block states after upgrading old worlds.