Unless they've changed how the register works, as soon as you do a price adjustment by manual adjustment or via price match, coupons tend not to work.
A PM is also the "other deals and promotions" section that the coupon legal says it won't work with.
I think it depends on your CS. When they price-matched and the coupon didn't work he said it's cause they PM'ed it, and I said it works on ANY Blu $9.99 and up and they overrode it. So YMMV I'd say