You're probably seeing that behavior with Ctrl-A-A because you get most of those key-down messages (at least for whatever the first two keys that are pressed, and then the keyboard controller resets itself and toggles the RESET line. You never actually get the key up messages. maybe. I haven't fully figured out the capabilities of the code provided here...
I'm working on new firmware which has slightly different wiring, to improve compatibility with A1000's speed and the A2000/3000 keyboard behaviors. -- Clock and data connect to pins D0 and D1 instead of D8 and D9. I am not yet ready to share this, but i will post on this thread when i am.
A2000/3000 have a different reset (ctrl-a-a) behavior than the A500.. You can simulate this by disconnecting Q1 from the circuit on your keyboard's controller. It won't be necessary for mine...