Okay, can you do the following...
Fire up kodi and enable debug logging.
Open the log on your pc (/storage/.kodi/temp/kodi.log)
For each of the 3 buttons:
1. Press the button.
2. Refresh / reload the log straight away.
3. Look at the last few lines of the log - there should be a couple of lines describing what you've done (maybe even the last 2 if you're quick and the button's not doing much).
So you end up with something like:
Quote
Exit button: (that's not in the log!!!)
Keyboard: scancode: 0x0e, sym: 0x0008, unicode: 0x0008, modifier: 0x0
DEBUG: OnKey: backspace (0xf008) pressed, action is Back
for each of the 3.
Post up the results.