For clarity; if both locks are in the unlocked position, locking only one lock only prevents entry from that particular handle. Both locks will separately need to be locked the key to restrict entry.
This also means that to gain entry, you would only need to unlock 1 lock. It takes some getting used to, but I prefer this type of lock - if you forget to lock the handles you just used to gain access, the other remains locked to someone who may pull the handle to check if it's open, and is unlikely, if he found it to be locked, he would try the other handle.
This handle and lock mechanism are quite nice, though, and do not require a lot of pulling force to open, like the style often seem in other boxes with the square shaped lever.
