I answered this question over at SE a few months back:
So someone comes along and edits it (How deleting a single tag is not considered "Too minor" when there are obvious gramatical errors all over the post is beyond me...) which puts the question back on Page 1. Someone comes along and downvotes my answer, after it was accepted and it's definitely correct.
Once an answer is accepted, shouldn't it be locked to prevent this? If it's accepted, it was presumably helpful to the OP and I think it should be immune to downvotes. Someone else can certainly come along and add their comments if they feel they have another answer, or add a comment to the accepted answer explaining why it may not be relevant or whatever a downvote on SE is supposed to signify.