Sorry, I was talking about Arduino Due.
As far as I know, the Due is kind of special as there is a magical baud rate of 1200 to bring the device in the programming mode. In that case, the Due will reset. One can prevent this behavior on Windows by suppressing the RTS signal, but on macOS (I even think on unix systems) it’s not possible due to the driver implementation.
That’s why I implemented a workaround. The controller does no longer reset when connecting with baud rate 1200. In addition I introduced another magical baud rate of 1800 to force a reset.
Typically on a Due it does not stand out, as the board is powered on as soon as the USB cable is plugged in. On my custom board, I do have a different schematic as I do not want to power the device on, while charging …
Anyhow, didn’t want to make it more complex 
Just wanna say, that the AVR programmer also pops up as two usb devices 