Using mgetty -r and minicom, mgetty does not print /etc/issue to the minicom screen.
Do you get the issue file after you press enter a number of times? Are you sure the connection is established? The man page / info page states that the issue file will not be printed until mgetty is sure that the connection is established when '-r' is used, so I suspect that this is the intended behaviour. Please read the info page, and if your experience is different than described, reopen the bug with more information.