Being position dependent makes absolutely no sense there.
Just to rule things out can you:
1. Put these 4 buttons into a blank scene and see what happens there.
2. You're not changing the sprite from the button right? If you are, please turn that off to see the effect, if any.
3. Is there a rigidbody on the button? If not, try adding one, and set isKinematic = true.
4. What if you remove the target to the button? So basically, make it so the buttons press but don't actually do anything beyond that.