The icon for stairs in the player's selection bars (hotbar, inventory, chests, etc.) in gamemodes Survival, Creative, and in Hardcore are mirrored 180 degrees. This is present in all versions of 1.9 present so far.

What I expected to happen was...:
The icons for stairs would have their normal pre-1.9 look.

What actually happened was...:
All stair icons in version 1.9+ is a mirror of its original pre-1.9 appearance. Please check the images for reference.

Steps to Reproduce:
1. Go to your inventory and find any kind of stair block. It's recommended to go to creative for testing and find the stair icon, but Survival, Adventure, and/or Hardcore is allowed.
2. If you compare one of the icons now (1.9 and 1.9.1 pre-releases) with a picture of one of the previous icons (from versions before 1.9), you will instantly notice that the image has been flipped. Please check the images for reference.