Hm, very interesting: env looks different in all consoles that start automatically with KDE, e.g. yakuake and consoles from the
last session. In these consoles KDEDIRS is set to "/usr/:/opt/kde3/". But when I start a new console via alt+f2, then KDEDIRS is
set to "/usr/" and the console looks even different (other background color). How can that be?

Well, in both consoles PATH does not include /opt/kde/bin. :(

Regards,
Stefan