There seems to be a problem with registering a cookie. I don't know if this is a WordPress problem but so far, 2 people have reported such a scenario and in the same post.
Basically, when they come back to comment, their name and email address is there in the comments portion already. The only problem - the name and email address is not theirs.
In my case, you may want to take a look at my post. Take a look at the comments area. There is some discussion regarding this problem too. You can comment in that post regarding this problem to ask viv and milky more details, I don't mind if the comments went out of topic.
In that post, milky actually saw viv's email address and successful posted as viv (accidentally). viv got a chance to post as me (Mr. Dew) too.
viv's email address got revealed to milky and the text "Mail (Will not be published)" meant little if his email address may be revealed to milky.
It is probable that SetCookie (not sure if this is the function name) register the wrong cookie to the wrong computer.
Once again, I don't know if this is a WordPress or PHP or web host problem. I don't even know how can this bug happen. I will be posting it to WordPress Mosquito later.
Any suggestions, work arounds or updates on this issue would be appreciated. Thanks.