I realize I'm replying to a comment from October, but when I was in BBB today, I was looking at the cashier's screen after I swiped my HC, and saw a pop up. It said something like "Authorized Value Card," and the cashier had to click on it before the transaction finished. I had no problem (churned 3 $50 HC for Disney in 3 separate transactions), but it looks like the system does have a way to distinguish prepaid cards like Happy Cards from true credit cards.
My guess is this is very much a YMMV situation regarding the instructions the cashiers are given for dealing with the pop up, but as I've had no trouble churning HC for other gift cards, I was surprised to see my store does actually have a pop up.