In Footprint Editor->Dimensions->User Grid Size: The labels next to the entry boxes for the Origin X/Y don’t change when the unit radio buttons are toggled. The units entered do follow the radio button settings so it’s not a bug that limits function, just one that adds some confusion. Perhaps the labels are hard-coded and could just be removed?
It would actually be nice to select the units of the grid spacing and origin separately, but I’m not holding my breath ;).
My version:
Version: 0.201512011501+6337~38~ubuntu14.04.1-stable release build
Bug is probably a by-product of: https://bugs.launchpad.net/kicad/+bug/593992