When running KDE from KDM login, environment variables from /etc/env.d do not get set, resulting in multiple problems such as kdevelop not finding Qt Designer.
All our current startkde's start a login session, which should inherit env.d settings. Check if your $KDEDIR/bin/startkde has #!/bin/sh --login, if --login is missing that is the source of the problem. You can either add it manually or [re]emerge the latest kdebase.
Similar bugs: http://bugs.gentoo.org/show_bug.cgi?id=4313 http://bugs.gentoo.org/show_bug.cgi?id=4955 http://bugs.gentoo.org/show_bug.cgi?id=5629 http://bugs.gentoo.org/show_bug.cgi?id=5683 http://bugs.gentoo.org/show_bug.cgi?id=5699 everyone has something diff to say ... think it should all be wrapped up and put into 1 bundle though ;)
I think my latest comment closes this bug, and since there are so many no reason to keep them all open. I'm closing this so that any further relevant comments can go into the main discussion at #5699. *** This bug has been marked as a duplicate of 5699 ***
Changed the shell for /etc/X11/xdm/Xsession and /etc/X11/gdm/PreSession/Default to "/bin/bash --login". Please check the ChangeLogs, and then remerge them (xfree-4.2.1-r2, gdm).