I got someone else with a Windows PC to try it, and it seemed to be working for him. I laughed when he used Labview to decide whether or not it was working :)
After I googled around a bit, I stumbled across hints that rebooting the host might resolve it, so I did and it is now connecting again via the USB UART on the pytrack board. I've just been able to sync the 3 libs across and still have the REPL up. Will post back if there are other developments.