I think I'm going crazy...
Small summary of all the little problems:
1) XKBD launched from terminal or .desktop file works if CAPS is ON (thanks for the hint pushwall), but kills Dpad upon exit and makes impossible to "click and select" or "click and run" in some apps
2) Rubybox seems to forget settings previously modified (thus making impossible to proceed by trial and error in fine tuning Dosbox)
3) there are some xkbd keys with weird bindings, ALT is recognized as SHIFT and ENTER as DOWN
4) the Dpad UP is interpreted as a Prtscrn, the LEFT as RIGHT ALT, the other 2 directions as "unknown keys" and binding them only works for one session

I'm starting to think my N800 is possessed