Here is an example of a question with an accepted answer that should not have actually been accepted:
How bitter is Robert Lustig's "Bitter Truth" about sugar?
Granted, the question itself isn't very good because it's asking about multiple referred claims. The comments are essentially correct in that the subject is not on a crusade against high-fructose corn syrup, but sugar in general. Having read his book, if I recall correctly, he doesn't really make a differentiation between HFCS and other forms of sugar.
It doesn't seem to me like this answer should have ever been accepted in the first place. Has there ever been a case where a moderator has unaccepted someone's answer, or is this something we will ever do?