Hrmm ... shouldn't -- since the whistle should be flagged as being a "status purchased" item; it should rebate your Personal Status and give you nearly the coin you paid for the horse.
Still ... be interesting to see if they missed that detail, somehow.
Also, if you buy your horse before your guild hits a "cheaper horse" GL, you can sell back your normally-priced whistle (getting most of your coin back), then buy one of the coin+status whistles. Let me tell you, for the 9p horses ... it's pretty nice to swap some personal status for a few plat.