We have found out that this is related to a chrome pop-up setting.
If you click on a link while linkvalidator setting is enabled, Chrome will show up the "pop-up" blocked message indicating that the linkvalidator page is blocked from being opened automtically. The problem is that linkvalidator is already being opened regardless. So if the user chooses "Always allow pop-up", clicking any links will open the page twice henceforward.
That being said, we do not think this is a bug related to the HTML5 chat. This rather seems to be a Chrome Browser issue, especially since no other browser is doing this behavior.