We are veering into off topic territory here! 
What you are seeing there is not a bug, but intended markdown behavior. Two asterisks surrounding text displays the text as italics. Because it includes an @ it is displayed as an invalid @username. Once you surround the regex in backticks it displays as preformatted text:
Italics with username: /.@service...cn/
Preformatted text: /.*@service\..*\.cn/