Documentation and mutating PGresult objects

"PGresult objects are read-only after creation, and so can be passed
around freely between threads."

From http://www.postgresql.org/docs/9.1/static/libpq-threading.html

But what about things like PQsetvalue? Is that a documentation bug?
Should result objects be protected by synchronization as well as
connection objects?

Regards,
    Jeff Davis