Well, this blows...and I don't know what happened.
I had the refurb page open.
I clicked refresh, and the 600ex-rt showed as available with Add to Cart enabled.
I kept trying to add to my cart, but it wouldn't. I tried with 2x different browsers...still no good. Other items I could add to my cart.
Then after many refreshes and trying this over and over....ad updated and now you can't add to cart.