The modifier is not recognized and it can't be used in combinations with other
keys under KDE (maybe others).
The problem is discussed on the KDE Buglist (somewhere after the mouse
The patch is also linked there:
Is is reported for XFree4.4.0 but I seem to have the same problem for X.org
(test2 build from ArchLinux - http://www.archlinux.org).
I haven't compiled xkb with that patch to see that it works also on X.org.
*** This bug has been marked as a duplicate of 587 ***