Well, I bought another pair of WH-701 and they do work with my N9. Probably the first ones were not original.
@linuxovod: maybe you should plug them with a one, smooth move? The difference between headset and lineout is that headset uses 4 pins, and the lineout - only three, the one closest to the cable is as long as two pins of the headset. So when you plug them not smoothly (I do not know how to describe it) you probably connect those two pins in the device with the headset plug (or maybe something inside your plug is wrong and there are some unwanted connections?).
I know, that you ask for something else, it would be more helpful if we could force it with a terminal, but I do not know the answer for that.