Sounds like the same symptoms I had a while ago. In my case, I was trying to get VNC server to accept mouse clicks properly. I read on the net that the problem was caused by an X-Windows input extension which allowed the tablet to detect pressure on the screen and differentiate finger taps from stylus taps.

The suggestion was to disable that extension, so I tried it. The side effects are exactly like what you're describing. The Fn key stopped working, as did the Chr key. I assume the same input extension handles those as well. It might have been a viable suggestion on an n770 or n800, but it's no good at all on a tablet with a physical keyboard.

You can check for this by looking at /etc/init.d/x-server. There's a line near the top that lists the arguments given to the server at startup. If that line contains "-extension XInputExtension", then the extension is disabled. You should be able to remove that part of the line and reboot.

For the record, the x-server args on my n810 are:

As far as I know, this is the standard configuration.