In this site, tagging a user does not send any notification to the user. Also if you post a comment in an answer or question that is not mine, I don't get notified either. So I just happen to see this.
Now I understand the issue. The TAG mentions in answers and comments are creating new tags in the question. This seems to be the original author's desire. It doesn't make much sense, IMO. I've adapted it so that tags can be REFERENCED in the answers and comments but only CREATED when asking questions.
I also fixed an issue. When creating a multiline post with a mention, the new line characters disappeared and a single line of text was displayed.
Please, redownload and let me know if it works as expected.