The Great (Train) Toilet Conundrum

I'm sure I'm not the first person to wonder about this, but why do they have three buttons to operate the door on a train toilet? There's an 'open door' button, a 'close door' button and a 'lock door' button. So... who exactly is there out there that wants to go inside the train toilet, close the door, but not lock it? I am struggling to think of a single scenario in which that particular option would be useful.

Presumably it would be just as easy to design the buttons so that the 'close' button also automatically locks the door, so someone, somewhere made a conscious decision not to do this. Any suggestions why?

Addendum (05/05): After dicussing this with Andy at lunch, we came up with one plausible(ish) explanation for why someone might decide to do this: if the button automatically locked the door, then pressing the button on the way out with have undesirable consequences. Of course, there are about a thousand ways these undesirable consequences could be avoided, and none of them seem as undesirable as the current worst-case scenario, but it is at least a plausible way in which someone might have stumbled across such crappy design.

Completely Inane Newspaper Stories Part IV: Dogs again

According to this shocking piece in the Salisbury Journal:

POLICE in Ringwood are investigating the circumstances surrounding an injury to a dog’s nose.

Well, what more is there to say? You can read the article for yourself if you want more details. Do remember to read the comments (incidentally, this reminds of this recipe for salted water that Steve Landsburg linked to a couple of months ago (again, read the comments).