Just a quick note here,

I was also using shift+space for tab and found it works everywhere else other than xterm... but the important thing for me was that changing shift+space breaks the page up functionality in browser. I currently have tab set to fn+backspace (shift for delete) and it works fine for me, reverted shift space to allow for pageup.

Thanks for the setxkbmap trick! I was using kill hildon-input-method for it to reload the maps, this way is much more reliable and safer