Falling down half blocks even with shift pressed

Description:
Sneaking downwards half a block (e.g. stairs or slabs) at the edge with pressed shift-key causes the player to fall off.

What I expected to happen was...:
To go one step downwards but staying on the stairs

What actually happened was...:
Falling down from the edge

Steps to reproduce:
1. Build stairs with stairs or slabs as shown on the attached screenshot
2. Try to sneak along one edge with shift-key down
3. fall off

Seems to be equivalent with:
#MC-5272