I have solved this question by myself.
Finally I found a great post with interesting topic.
What language is your forum set to?
Yeah, seems to be a language problem (probably a newline got misplaced in a translation somewhere). Depending on what language your forum is using, you can fix it here: https://transifex.com/projects/p/nodebb
It's set to en_US.
Thanks for another quick quality of life fix. It's appreciated!