...and just now I have neither time nor nerve to look for a fix. "O" apparently is transmitted as enter, the left mouse button opens context menus, and so on. Neither a VNC restart on the remote machine nor a KRDC restart change anything - I've had that problem before (maybe it's the compressed ssh tunnel). Most forum and blog posters complain about apparent tightvnc bugs, but for me, switching to a different viewer already did the job.
Usually, the KDE3 KRDC version is less buggy (look for package kdenetwork3-vnc), but if you need just a plain vanilla VNC without extras like full screen windows and special key transmission, tightvnc's vncviewer (package tightvnc, binary is /usr/bin/vncviewer) has a nice minimalist interface (no space-eating menus). The -fullscreen option is also very useful.