There is nothing against the rules to retract bids. Have you not ever walked around a store picking things up, then change your mind on something and put it back on the shelf? It's far better having someone retract a bid than have them change their mind after and you have to go through the whole unpaid item route, which effectively ties your item up for 8 days.

My guess is both your bidders changed their mind if they were the only bidder. They may have found the same item cheaper. Others will put a bid on to try and find what the highest bid is and then retract. If you look at their history they have a high retraction rate. EBay says they frown on people who do that, but you can report all your like and nothing ever happens.