Having exactly the same issue. Running Mavericks. Once flashed, the Edison will sporadically disconnect and then start up. It wouldn't show up in Finder as a drive. So reset mac and seems to work, still cannot screen in.
Curiously, I have also tried opening ArduinoIDE and actively choosing the board from the ports. Attempted sketch upload, but arduino returns error; saying that the selected port is already in use and to close any programs using it. So I restarted Mac again (without re-flashing the Edison).
Now if I open Terminal or Arduino first without flashing, the port is available and uploads sketches, also can screen in.
I am wondering if finder is still using the port once the flash is complete thus making it impossible to screen in?