Can't switch to serial console except at opening screen

[JamesNewton]

The serial console is an AMAZING feature of the badge! Wonderful for loading files, doing extensive setup work, etc... It really helps to overcome the natural limitations of the keyboard.

For whatever reason, I find that I'm not able to switch into the serial console mode /except/ at the opening menu.

If I go to CP/M and then hold both shifts and press BRK/COL the local keyswitches stop working, but the serial console doesn't respond. If I switch back, the local keys start working. It seems like something is happening, but the serial port isn't fully engaged.

If I do that at the menu, it works fine and I can switch back and forth as much as I like.

To reproduce (or not, let me know either way please)
https://hackaday.io/project/161859-2018-hackaday-superconference-badge/log/154556-serial-communications-with-badge

Connect a USB to serial converter to the badge pins: C13 to TX, C14 to RX. Connect ground but not power. Set your favorite serial terminal program to 19200 N 8 1 and configure a LF after CR. Reset the badge (hold both shifts, press RESET) then switch to serial terminal mode (hold both shifts, press BRK/COL). Select option 2 (press Enter or Ctrl+Enter).

In CP/M verify serial operation. Then hold both shifts and press BRK/COL to switch back and verify keyboard operation. Then switch back /again/ and see if the serial operation continues to work. On mine, it does't. I've tried RealTerm and PuTTY with the same results. Resetting / power cycling the USB-serial converter has no effect. Restarting the terminal program has no effect.