function 12 and volume keys flipped

i have a new 15.4 2.53.

I have a question, by default. When you press the key 2nd in on the top right, which is also volume up and f12, when you press it on its own, is it supposed to control the volume or control the f12 assigned in expose for example.

Mine was working normally it was controlling volume as i expect it. now all my top fn keys contronl fn if you press them on thei own.. to control volume i have to press fn ? that does not seem right, what has happened?