It seems strange that nobody has mentioned the possibility of the pitot cover being left on or a bockage of the pitot head and drain hole by ice/insect eggs.
That being the case, the ASI would act in the form of an altimeter and over-read in the climb.
Obviously, in visual conditions the increased nose attitiude would ring alarm bells but this could be extremely dangerous in IMC without the usual visual clues. I would be very wary of assuming that a stall warner is incorrectly set just because the ASI reads what is expected; it is also worth remembering that the stall warner is set to sound well before the stall, not at the point of stall.