Please, try following:
delete the xmodmap line from .xsession and run it manually after X11 startup.
Why? My ion3 complains that X does not know XF86*** keysyms after startup,
but when I restart it (only ion3), it doesn't complain anymore and loads
its keybindings properly. Maybe it is related, maybe not.
--
Tomas Ebenlendr
http://drak.ucw.cz/~ebik