Unexpected double output in setup() - Why???

krupski:
Try this:

int main (void)

{
    init(); // performs timer and interrupt setup
    Serial.begin (9600); // setup serial port
    while (!Serial); // probably don't need this
    Serial.println ("Serial Monitor initialized..."); // print message
    while (1); // forever loop (main has nowhere to "exit" to).
}

Double output...