Knocks Out USB Ports?

We're in Day 2 of using Arduino Nanos with MacBook Airs running 10.10. We're trying to successfully complete the first basic lesson--getting the light to flash. We have the software installed successfully, the correct board selected and the correct port. We discovered yesterday after 45 minutes of troubleshooting that in order to have the test run successfully more than once, we literally have to unplug the board and switch it to the other USB port on the laptop. Then the code works again...once. Then we have to switch it to the other USB port...??? We contacted the folks at our local makers space group who have designed this program and curriculum for us (we're a middle school trying our first robotics elective), but they had no clue why this might be happening. Doesn't bode well for us since they were our experts in the field who were going to guide us through this initial course.

Any thoughts or suggestions greatly appreciated!

Same problem.

I was literally about to post a topic on this then saw yours! I am having the exact same issue except with windows. I wrote a small program for the Micro (which works great!) but the trouble is, if the Micro gets disconnected from the port, it kills the port (as in I can no longer plug ANYTHING into that port until I reboot the computer). I'm guessing there is some obvious driver issue that is not releasing the port when the Micro is unplugged.

Anyone else know of similar behavior or a potential solution? The Micro is based on the Leonardo and uses the AtMega32U4 which has the built in USB functionality (which my project takes advantage of).