I tried to reply to a user by way of comment on my answer, which normally I do all the time to make sure they get the comment, but this time, when I tried, I got the generic "Comments cannot contain this content" error.

It appears that their name may be the issue (it's "Алёна Опарина"). The system allowed me to auto-complete the name when I typed @, but when I try to post it, it gave me this error. This is question that was posted.

I also tried several variations of the comment, and all of them were rejected, so I suspect that this is a problem with the username and not anything I've tried to say. I've also never had this problem with similar comments on any other comment I've written, hence why I'm asking.

Is there somewhere we can see the list of disallowed phrases? Should the system block a comment because of the username?