Hm, is /USR actually in caps, or did you change that for emphasis?
> I'm at a loss as to where the /USR came from. > It's not in config.log (compile time) > nor in the psql executable (run time).
I think it came out of /etc/ld.so.conf.
BTW, by default PG would link psql using an rpath switch pointing at /usr/local/pgsql/lib, which I assume is where your manual build put its libpq.so. That's evidently not having success getting that libpq.so to be used. Did you tell configure to --disable-rpath? Or maybe move the installation after building it?