I cannot seem to get the "auto-complete" pop-up to appear. If I manually write out the entire name when replying, the @Pedro bit simply disappears once the comment is posted.
Tested on several questions, and this seems to only be affecting AskUbuntu, and not the rest of StackExchange.
Tested using FireFox 26.0 and Ubuntu 13.10
You don't need a @ tag if you're responding to the owner of a post. It is discouraged, and thus removed upon submission.
From here:
The first author of the question or answer will always be notified of any new comment. There is no need to use @name to notify them. (You may still use it for clarity, if needed; however if only you and the author have been commenting on the post so far, the @name will be automatically removed from the beginning of the comment, as it adds no value.)
Further explanation here:
@lerting the post owner in a comment is not necessary. If comments are only between you and the post-owner, and nobody else is commenting, then an @lert to the post owner at the beginning of a comment will be removed.
