Comments always notify the original author of the post (which is who you were trying to notify) regardless of whether or not you
@name them. Therefore, if the owner of the post is the only other person talking in the comments, the leading
@name will be removed since it is redundant. So, basically, this is status-bydesign
From How do comment @replies work?
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.)