What we see with the eBay login page is that a certain number of invalid logins will lead to a "blocked" state which requires additional verification in the form of a CAPTCHA challenge (as you probably saw in the snipe confirmation page). It doesn't matter whether the invalid logins came from you, from us, from browser auto-completion, or from some other user (malicious or not). It doesn't even matter if the bad logins were all at once or over some period of time. Sometimes this is a globally blocked state and other times it seems to apply only to certain locations. eBay is trying to block malicious users and bots by changing the rules from time to time, but we occasionally get caught up by this extra verification layer.
When this happens, the blocked state typically lasts for a day or so, and unfortunately it can affect every login attempt. Our software is unable to provide the CAPTCHA numbers when challenged and the bid fails. This is fairly rare but it is troubling, and we share your frustration. We are working to handle these conditions better where we can, but we have to work within the confines of what eBay presents us.
Once the extra challenge is lifted, typically by the next day, bidding and sniping can resume as normal. Hopefully your account is back to a good working state by now.