Bug: Grafted Wargear

I didn't see anything in the rulings for this card in Gatherer, so I'm pretty sure it's a bug.
Grafted Wargear reads, "whenever Grafted Wargear becomes unattached from a creature, sacrifice that creature."
But when I unattach GW from a card, Forge exiles it instead of sending it to the graveyard. Kinda sucks because I built a deck based on the ability to send recurring weenies to the graveyard with GW and other sacrifice outlets and then bring them back.
Grafted Wargear reads, "whenever Grafted Wargear becomes unattached from a creature, sacrifice that creature."
But when I unattach GW from a card, Forge exiles it instead of sending it to the graveyard. Kinda sucks because I built a deck based on the ability to send recurring weenies to the graveyard with GW and other sacrifice outlets and then bring them back.