It turns out this works perfectly. So the two options are:
- Completely disable repeating keystrokes (so you'll only get one keystroke no matter how long the key is held down for). This works fine, but is a little irritating.
- Increase the time before a key will start repeating. I think the default is small (60ms) - make it larger and the problem should go away.
To get into the keyboard settings on Kubuntu, log in to KDE, go to System Settings and then Keyboard.