Hi yoda2nd,
perhaps you already did, but you may look at this page for further info: http://arduino.cc/en/Guide/ArduinoLeonardoMicro#toc4. I don't have a micro, but I understand that before uploading the sketch the Arduino IDE resets the micro, which creates a new virtual port (the micro has no separate controller for serial communication). I understand that in the IDE the timing between the reset and the launch of avrdude is based on some previous trial and error, not "exact science".
This explains why disconnecting the micro works for you (a reset should produce the same effect), and the fact that you have to find a timing that works for you before pressing upload, allowing for the new virtual port to be recognized by your OS, but with the micro still running the bootloader. The most likely reason why avrdude hangs is that it's trying to communicate with a micro that is already past the bootloader stage.
I take this opportunity to thank Jantje for his excellent plugin. Nice to know he's still monitoring this thread.