`@` sign triggers username replacement when it is not desired

To reproduce, create a comment on an issue containing text @1x .
This matches a username, therefore it is replace with that user's full name, and displayed as @Aliaksei Verkhaturau

In my case, we have many comments that discuss images at different zoom levels, and therefore often encounter comments like "See @1x version of image". For my team and our clients, the end result is that our information is modified to be quite confusing. We would want the replacement for usernames that we know of, but not for total strangers.

(Note that to get this description to display correctly here in the Issue Tracker, I had to escape these terms using backticks. This would not be a realistic solution to apply elsewhere.)