youngRobot,
Thanks for your reply.
However, as I said in my first post, it doesn't look it's due to "auto-repeat". I say this because it is not a repeat that I'm seeing, it is more like the buffering of the previous entry - even if I wait a few minutes and press a key, I often get a return value for previous key. The next return will be correct. (I am getting only 1 return / key) It's weird.
I almost wonder if it has something to do with using delayMicroseconds() in the interrupt. I know it's better than using delay() but I think it disables interrupts - not that I can relate that to the problem!
Anyway, it's a mystery to me.
So I take it that you don't see the problem using your test sketch?