I’m not sure what is causing the problem. As Dan says, it is quite possible for something else that accesses the serial port to cause a problem, and the fact that it works on Windows suggests that this is the case, rather than a genuine hardware issue. And… I would have suggested looking at different USB ports next, if you hadn’t already tried it. Do you have any “unusual” software or settings that you might be able to identify?
Since you’re local, we could also consider testing it here (or exchanging the EBB), on the off chance that it is actually a hardware issue. There are some subtle differences between USB ports on different computers, and it is conceivable (but unlikely) that there could be an intermittent hardware issue that can only be seen on a mac.
