I did have my card thrown into a fraud alert. They were concerned with three charges. #1: $5 at a small grocery store (lunch). #2 $160 at Kroger to verify the $100 gift card earned 4X points, plus a gas card and some groceries. #3 (a few hours after #2) $350 in gift cards did not get approved. Got an immediate e-mail from Amex to contact them. I have a second BC Preferred, so I used that one.

They might have seen - small charge to make sure card works, then gift card buys and locked it down - typical MO of fraudsters as I understand. It took about two minutes to get it resolved on the phone. It might be a good idea to let Amex know ahead of time if you try it. They might be happy with it since they get to double dip by charging both the grocery store and the restaurant transaction fees.