I never knew about the function keys on the Franklin Ace 500/2x00. That's really cool. I wish that I'd had one of those back in the day just for that feature.
Perusing the code, I made a few modifications and the function keys seem to work, (at least on initial testing, not extensively tested though).
I think the problem is that it hits the strobe when you press the key AND when you release the key and there's no key down so it returns 0 and basically types the @ symbol.