Sneaking doesn't protect players from falling into gaps of 0.625 block wide

If a player is sneaking on the wall or fence and walking toward the gap of 0.625 block wide (made by other wall or fence), the player will fall into the gap.

The first three images are examples.  This problem does not happen in the fourth (a gap of 0.625 block, made by a grindstone and stairs) and fifth (a gap of 0.6875 block) images.