What I expected to happen was...:
A small gap is made in the corner made by connected stairs and is not part of the hit box; this makes it possible to access hidden chests behind the walls.

What actually happened was...:
The stairs take up an entire full block hit box, making it impossible to utilize the gap in the stair.

Steps to Reproduce:
1. Placed chest and placed stairs (first noticed error with cobblestone stairs in 1.9)
2. Retried same setup with every single type of stair (none will work in 1.9)
3. Verified that 1.8.9 gap use is still possible and tested previously-made constructions utilizing this feature (I was able to open the chests with no problem through the hit box gap in 1.8.9)