I have just observed that my reply to a comment has appeared twice: the first time with my username and then second time as "Anonymous Monk" (the node is Override printing to STDOUT/ERR).
What I suspect I did was
2) write the comment
3) preview comment
4) clear cookies (via browser clear history, not logout)
5) clicked create.
Most likely this is a false alarm and I am trying to reproduce it here. It could well be that I have posted while cookies were valid, then cleared the cookies and then reloaded the page and somehow posted exactly the same as anon.