I have replaced KDE4 with XFCE, solving some issues but not this one. Some additional searching resulted in the addition of the hid_ntrig module to /etc/modprobe.d/blacklist.conf. The N-Trig Duosense Touchscreen built into my Thinkpad 410s seems to override mouse/touchpad/touchpoint input events, thus making the system unusable until X restart. No idea if this should be filed as X or kernel bug, but it certainly is not a plasma bug.
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