That was it, thank you! I had installed some fonts using Peter Schaffter's marvelous install-font script, which generates a download file in /usr/local/share/groff/site-font/devps/. But I should have added the entries in the distribution's devps download onto the one generated by the script. I overlooked the phrase in the devps man page: "The download file itself is also sought using this mechanism; currently, only the first matching file found in the device and font description search path is used." Once I did add those entries, the ps output is correct again. Naturally, I didn't see that behavior with gropdf, because SS is not downloaded, but is generated with a script.
Sorry about that. Peter, you explain very clearly that the system download file has to be updated, when you set out how to manually add fonts. The install-font script generates its own download file -- would it be worth stating, for dolts like me, that it is essential to copy the system download file into that generated file?
Thanks - Robert.