Hello
Petzl has identified a quality issue with a limited number of the M34 BL Am'D BALL-LOCK and M36 BL WILLIAM BALL-LOCK carabiners with the new metal locking sleeve: the sleeve may be unlocked without pressing the green button, so the locking system acts as a TWIST-LOCK, instead of a BALL-LOCK.
Please see
http://en.petzl.com/petzl/SportNews?News=149
for details
Hank Moon
Technical Information Manager
Petzl America