the only thing i can think of is that the bulb you have bought is a single filament bulb when the stop lamp on the stilo is a double filament bulb.
This is wierd as it shouldnt have gone in, but i have had this happen on a seat ibiza
It is a double filament, both regular and stop lights work, but warning goes on as I press the brake pedal - strange... and frustrating, may be I'll buy another bulb...