What PG version are you using and did you try to upgrade it (and rebuild PHP with the upgraded libs) ?

I have tried and can repeat the error on the following:

Fedora Core 2 (x86):
 PHP 5.0.4* PG 8.1*
 PHP 5.1.2* PG 8.1*

Fedora Core 3 (x86-64):
 PHP 5.0.4** PG 8.1*
 PHP 5.1.2*  PG 8.1*

* = compiled from source
** = system RPM

 I also doublechecked that the connection only says its busy if the previous query had an error (ie change the query to a valid SELECT and it doesn't happen)

Please try using this CVS snapshot:

  http://snaps.php.net/php5.2-latest.tar.gz
 
For Windows:

  http://windows.php.net/snapshots/

No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

Edit: We gave up on Postgres for that project, but had to revisit this recently; the issue still exists but it seems the cause is actually that pg_connection_busy() stays true for some time after a query that causes any sort of postgres error.

Tested additionally with
x86_64/FC10 + PHP [5.2.9 | 5.2.11 | 5.3.0] + Postgres 8.3


#!/usr/bin/php
<?php
    $connStr = sprintf("host=%s dbname=%s user=%s password=%s", 'localhost', 'testlevi', 'levi', 'levi');
    ($dbConn = pg_connect($connStr)) or die("Could not connect");

    @pg_query($dbConn, "drop table thisTableExists");
    @pg_query($dbConn, "drop table thisTableDoesNotExist");
    pg_query($dbConn, "create table thisTableExists (x varchar(255))") || die("Can't create table");
    pg_query($dbConn, "insert into thisTableExists values ('foo')") || die("Can't insert first row");
    pg_query($dbConn, "insert into thisTableExists values ('foo2')") || die("Can't insert second row");

    $loopCount = 0;
    while (true) {

            // First 20 queries are completely valid; after that we try invalid queries

            $sql = ($loopCount < 20)
                ? "select * from thisTableExists; select * from thisTableExists;"
                : "select * from thisTableExists; select * from thisTableDoesNotExist;";

            // Issue the queries
            pg_send_query($dbConn, $sql);

            // Check first result
            $result1 = pg_get_result($dbConn);
            $rowCount1 = pg_num_rows($result1);
            if ($rowCount1 != 2) die("Bad result set returned (1)");

            // Check the second result
            $result2 = pg_get_result($dbConn);
            $rowCount2 = pg_num_rows($result2);
            $expectedRowCount = ($loopCount >= 20) ? 0 : 2;
            if ($rowCount2 != $expectedRowCount) die("Bad result set returned (2)");

            if (pg_connection_busy($dbConn)) {
                echo (pg_connection_status($dbConn) == PGSQL_CONNECTION_OK) ? '+' : '-';
                while (pg_connection_busy($dbConn)) {
                    echo '!';
                    usleep(1);
                }
            }
            echo ".";
            $loopCount++;
    }
?>

Expected output:
........................... etc
Actual output:
....................+!.+!.+...............+.+!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.....+!.+!.+!.+



Comments for anyone else experiencing this:

It seems pg_get_result() correctly waits until results are ready, but even after pg_get_result() returns, if there was an error in the query then pg_connection_busy() will stay true for some time.