Problem solved by removing ~/.trinity/share/applnk/kpdf_part.desktop which had contained:
[Desktop Entry] Exec= MimeType= Name=KPDF Terminal=false Type=Application X-TDE-InitialPreference=17
Google seems to suggest that applnk was a pre KDE 3.2 menu structure. That's a long time ago and I don't know how kpdf's applnk got into my ~/.trinity. There are no other applnk files.
Thanks to everybody who provided helpful clues.
--Mike