It is kind of annoying when you are trying to leave comments on other's sites. I realize that everyone's answers are unique. It can't be helped that one would say the same thing as someone else.
I think that is what they look at when you comment on someone else's site. It does prevent everyone from saying the exact same thing.

Yes that sometimes happens to me too. It does get very frustrating. If it happens a couple of times in a row I just go on and do something else and come back later.