Walls don't stack properly in some directions when placed next to blocks

When you place walls on top of each other next to a block, there is a small gap. Causing a block update causes the gap to go away. This only happens when the upper wall is placed first, and it doesn't happen when the wall is placed to the east of the block.

What I expected to happen was...:
When placed on top of each other next to a block, walls should not have a gap.

What actually happened was...:
There is a gap between the walls.

Steps to Reproduce:
1. Place a 2 block tall pillar.

2. In any direction except east, place one wall adjacent to the upper block.

3. Place another wall below the first wall. Now there should be a gap between the two walls.

This could be a duplicate of MC-170846