DBD::Pg errstr method doesn't return full error messages

Hi, I'm using DBD::Pg version 0.98 with Postgres 7.1.  I'm noticing
that quite often on an error, the $dbh->errstr method doesn't return
the full error.  For example, if I have a table with a unique key
constraint:

CREATE TABLE urls (
  url_id SERIAL PRIMARY KEY,
  msg_id integer NOT NULL REFERENCES msg_info(msg_id),
  url_link varchar(255) NOT NULL default ''
);

and I do this insert:

INSERT INTO urls (msg_id,url_link) VALUES (9,'http://www.kcilink.com/');

the second time I insert it, I get this on the psql command line:

ERROR:  Cannot insert a duplicate key into unique index urls_id_link

However, if I use a perl module to do it, like this:

  my $sth = $dbh->prepare('INSERT INTO urls (msg_id,url_link) VALUES (?,?)');
  if ($sth and $sth->execute($msgid,$url)) {
    ($urlid) = $dbh->selectrow_array("SELECT currval('urls_url_id_seq')");
  } else {
    print $dbh->errstr(),"\n";
  }

where $msgid and $url are the same values above, I get this output:

ERROR:  Cannot i

This makes it a bit difficult to distinguish between a hard error and
simply a duplicate insert error, which I can handle in this app.

Also, at other times, I get just "7" as the error message rather than
the full message, making error reporting just a bit confusing. ;-)

Do you know of any issues with $dbh->errstr that could be causing
this?  Any workarounds I might try?