I know less than nothing about Button Mapper. So going on the rash presumption that it's not the problem... Just make sure under Android Settings > System > Languages > Physical Keyboard > that it says "Default".
When you connect any type of keyboard there should appear something in logcat saying what the device is and what keylayout it decided to load. Check that first for VID/PID and whatever.kl
Code:
$ logcat | grep attached
$ logcat | grep keylayout
Use my UsbMode.apk and see the "Linux Code" and the "Android Code" for what you are talking about.
http://www.temblast.com/usbmode.htm