Thanks for the suggestion, Lyndel. I've not spilled water on the unit, but it's possible condensation could have formed over time i guess.

The only thing that makes me question if this is an electronic problem is that the home button starts to work if I reset the unit's firmware and use the standard Phillips interface, and that all buttons beep when I press them.

I don't really have much to lose though, so no harm in trying out your suggestion.

I'll report back once I've had a chance to explore. If it doesn't resolve it, maybe I'll explore irule or similar as a replacement....