I have come across an intermittent bug when replying to user comments with the @replies feature using Google chrome.
Normally when replying to a comment, I can type '@' and the first letter or two of the user name I want to reply to, and am presented with the complete name (auto-completion), and pressing tab the user name is filled in.
But, I would say probably about 10% of the time, this feature does not work. I type the '@' and a few letters of the user name, but there is no auto-completion, so I type the entire name and then the comment. But when I submit the comment, the @username is not present in the comment. Every time this occurs (I have no idea how to consistently reproduce it), I try to see if there is something specific about the user name, but have found no patterns (special chars, spaces, dots, commas, etc).
This happened yesterday, but I didnt have time to report it then. The next time this happens, I will update this question/bug with the details so as to help debug the problem.
I have read the faq and this meta SO question, so I feel that Im familiar with the feature and using it correctly.
Edit: One more piece of info: Ive seen this on both windows XP and Vista.