Hi, you can find attached a couple of files generated by USB Prober on a Mac OS X 10.6.8, one for each behaviour (the names should be self-explanatory).
The "NoSerial" one is generated when on the Due is running a sketch (just a "SerialUSB.begin(115200);" and nothing else) uploaded with the IDE built from the fabc658a942de659d44f22f196701d04b857f094 commit.
The "SerialOK" one is generated uploading the same sketch with the same IDE, but after restoring the ">=8 patch" so that the serial port appears.
I hope this helps!
USBBusProbe_10.6.8_NoSerial.txt (13 KB)
USBBusProbe_10.6.8_SerialOK.txt (13 KB)