I have DBD::Pg version 1.49, and in its connect method, I see:

152                  my ($dbh) = DBI::_new_dbh($drh, {
153                          'Name' => $Name,
154                          'User' => $user, 'CURRENT_USER' => $user,
155                  });
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Maybe that has something to do with it. I don't see User used anywhere else (not that I've done an exhaustive search of DBI-related code), so maybe that's why the warning seems to be toothless.

Thanks for letting us know how it works on your setup!