I have tetex set up to use a local texmf tree /usr/share/texmf.local, in
which I have a font (in pk form) not a part of tetex. When I give a
"dvips" command directly, the font is found and used correctly.
I also have /etc/printcap configured by printtool to print to a remote
postscript printer, so the input filter calls dvips for dvi files.
However, when I give an "lpr filename.dvi" command, the font in my local
texmf tree isn't found, and cmr10 is substituted instead.
Resolved! I updated tetex to the latest version of the distribution and the
problem disappeared. (Of course, I still have no idea why the problem was there
in the first place.)
I'm closing this. Reopen it if your problem returns.