this is part of an ongoing post with DARKANGEL but i would be interested to know if i am talking crap or not regarding the tip of key being needed to open the lock or not (picking the lock will just cause the lock to turn around and around and do little)
I pulled apart x2 abloy protec Euro cly + turn today that were on the bottom of big glass doors - the tip of key pushes in a springloaded cam which then engages the black "arm" that rotates and unlocks the door. The problem today was that the holes were the locks fitted into was full of dirt (being on the bottom of the doors) and as such was compacted by the lock bolt. They forced the lock closed (due to the dirt) and had rounded of edges inside the abloy protec cly and as such the key turned around and around because the tip of the key (and the spring loaded cam) rolled over the black 'arm' because it had no square metal to 'hold onto'
there some cheap euros with "floating" black arms (cams or whatever you know it as) that can be opened with out a key engaging the back of the lock. Those with "fixed" cams (i.e. the are solid and only move only with the key) need the tip of the key to turn the lock.
i will post pictures on lockpicking101 if i knew how