Key wont come out of lock unless it is locked?

We have euro locks on pvs doors front and back. Front door will lock and unlock ok but will only give up the key in the locked posiiton. Switched locks with back door. Back door lock was the same in the front door and the front door worked in the back door!! Anyone any ideas where the problem is. I was told I needed a new barrel but it would appear it isnt the barrel. Fed up having to come in after unlocking the door and then having to lock it to get my key out of the front and then putting it in the back so I can unlock the door to be able to shut it. HELP!!