Hi, faced same issues on my HP laptop. In addition to your findings, I investigated following:
1. Problem caused by ktouchpadenabler KDED module, which is included in one of the latest KDE updates;
2. I did not found how to configure it, but found how to disable it: just modify /usr/share/kde4/services/kded/ktouchpadenabler.desktop to set X-KDE-Kded-autoload=false and relogin to kde (do not forget to set touchpadEnabled=true in ~/.kde/share/config/ktouchpadenablerrc).
After this action, Fn+F11 works as expected and do not affect touchpad anymore.
Last edited by ava1ar; 03-17-2013 at 10:48 PM.