Unfortunately, there seem to be three states for the "add to cart" button - greyed out because it's out of stock, orange because it's in stock and available for purchase, and orange (but when you click on it, you get a message that the lens in unavailable, and the button turns grey).
I've been keeping an eye on the refurb section for a few weeks. Immediately after I purchased Saturday, the button was grey. A bit later, it was orange again, and stayed that way for longer than I'd expected - so out of curiosity I clicked, and you guessed it - not actually in stock.
