I agree completely with Cellarseller. This isn't AS's fault - it's eBay. First, there's no reason for eBay to suddenly require a captcha when bidding, since manual bidders have already logged in. It must be directed at sniper bots. Why? Over the years I have received emails from other bidders (from a time when they could get your email) complaining that I had sniped an auction and "hadn't given them a chance to bid again." Despite the fact that they are clueless about proxy bidding, I suspect their complaints to eBay have caused this captcha nonsense. And as in Cellarseller's case, I lost out on an auction that had no other bids. Once again eBay is protecting the newbie bidders at the expense of sellers. If enough of us notified sellers that they missed out on a higher bid, maybe eBay will drop this nonsense. Otherwise AS's sporadic lockout renders it useless.
A better solution for eBay is what other auction sites do: an auction won't end until x minutes after the last bid. At least that way the newbie complainers have to be at their machines to re-bid.