Updated to KDE 4.6.2 on one computer and weird problem happened. When tried automount usb disk and open it with dolphin instead I got dialog to choose program to do it with. Strange. Later discovered, that right-click on file “Open With” dialog was empty. Just like all mime-related info was gone.
To fix it, just remove /var/tmp/kdecache-[username] and just relogin to KDE.