To reproduce:

1. Open the project, attached by the user (Collider2dOrderBug.zip)
2. Open the "Demo" scene
3. Enter Play mode
4. There are two sprites on the right of the screen, press the top one
5. Observe, how the sprite behind the clicked sprite chnages color instead of the clicked sprite
6. Move the Default sorting layer to be the last (first in the list)
7. Click on the top sprite again
8. Observe, that everything works as expected

Expected: raycast hits the sprite that is in the front

Reproduced in 2017.1.3p2, 2017.2.2p1, 2017.3.2f1, 2018.1.0b10,2018.1.0b12, 2018.2.0a5