Hi all!
I've just bought a new Arduino Micro board and it has a problem with the serial port when connected to Ubuntu pc.
When it's just connected I can see the serial in /dev/ttyACM0 but as soon as the green light stop flashing the serial disappear and appear as /dev/usbserial1.[something] and I cannot read the serial port. It's the same problem trying to upload the sketch on the board.
How can I fix it?
Thank you very much.
PS: under Mac OS X the board works fine.
I have this problem too, you are not alone 
but I don't know how to fix it, I just changed OS.