Situation:
OP post.
Reply from X.
The reply is proposed as answer by Y.
The reply is marked as an answer by the Moderator.
The reply is unmarked as an answer by the OP.
In this situation the OP has clearly said that he doesn't regard X's post as an answer, yet the post is still marked as Proposed as Answer.
This means that the Moderator on his/her next sweep of Proposed posts sees it again only to discover that he's already marked it and the OP has already said that it isn't the answer. Waste of the Moderator's time in other words.
In such a situation there ought to be an automatic removal of the propose as answer,
FAQ sites: (SP 2010)
http://wssv4faq.mindsharp.com; (v3)
http://wssv3faq.mindsharp.com and (WSS 2.0)
http://wssv2faq.mindsharp.com
Complete Book Lists (incl. foreign language) on each site.