Adding a serial port of the same host path, even if disconnected, isn't allowed.

[Jerome Poulin]

If you add a serial port with for example, Path: /tmp/box, then disable the port, add a new serial port in the second section, put the same path, it won't work telling the first (now disabled) port has the same path, you have to enable the port, choose Disconnected, and disable the port again.

[Frank Mehnert]

Minor issue, fixed in SVN.