Yes, it is generally assumed you would not tell a current job you were looking for a new job but do they have this box? The box forces the issue, makes it look like you could have something to hide; it's the kind of box that, when you see it, I think you should think twice about working for that place where you are applying.

You would not tell a current boss but that is not the question, the question is can we call them? :-) Devious.

If you think about it, they can do whatever they want, with/without the box; they are allowed to check up on what you write on the application so the question looks "nice" but that is not its purpose I don't think.