There is a fairly long chain of unconfirmed transaction from that address and while most of them do include fees the root transaction (https://blockchain.info/tx-index/75347434/1) doesn't.
I actually had the "pay fees" setting set to 'Frugal' for a bit (since I didn't have that much in the account), but I switched it back to 'normal' this morning before sending the second batch of bets and my other non-SD transaction. I'm not sure it has helped so far, but I figured I'd wait and see.
Much appreciated, and there's no rush so low priority isn't a problem. I was just more concerned for the reasoning behind the unconfirmed status than anything else.