Found while testing MCPE-170445.

The bug

For parts of walls that connect to horizontally adjacent blocks, there appear to be faces which are never visible without clipping into the block. These faces can be removed, and I believe they do not exist in Java Edition.

How to reproduce

1. Place a wall
2. Place a solid block next to it
3. Enter Spectator mode
4. Fly inside of the post

Expected results

The face of the part of the wall extending out from the post would not be visible from inside of the wall post.

Actual results

It is.

How to fix

Remove this face.