I tried to reply to a comment when I wasn't logged on as admin and I noticed that the name, e-mail and url fields were auto-completed with the previous poster's data. I have tried it on several browsers and computers, just to eliminate a freak cookie issue, but the fields remained auto-completed every time.
This is a huge privacy issue: name and website are obviously not a problem, but I don't want to leak the e-mail addresses of those who comment on my blog.
The problem went away after disabling the plugin.
Plugin Version 18.104.22.168, WordPress 3.1