euh, how do you figure that? That would be a MAJOR bug in SimC. I'm looking at the Sim done early this morning for patchwerk T14H warlock Affliction and it shows exactly 1 use of Shadowbite on the sim, from what I can tell.
What version are you using, and what made you think it's not sacrificing the Felhunter?
EDIT: You probably mean by simming something yourself, not the default Sim results. A lot of things could have gone wrong then, but we'd need version number and a description of what went wrong regardless.