Please try using this CVS snapshot:

  http://snaps.php.net/php5.2-latest.tar.gz
 
For Windows:
 
  http://snaps.php.net/win32/php5.2-win32-latest.zip

the current snapshot does NOT solve the problem - there are 
still all rows returned.

Thank you for this bug report. To properly diagnose the problem, we
need a short but complete example script to be able to reproduce
this bug ourselves. 

A proper reproducing script starts with <?php and ends with ?>,
is max. 10-20 lines long and does not require any external 
resources such as databases, etc. If the script requires a 
database to demonstrate the issue, please make sure it creates 
all necessary tables, stored procedures etc.

Please avoid embedding huge scripts into the report.

// prepare the database
$dbh = new 
PDO('mysql:host=localhost;dbname=test', 'test', 'test');
$dbh->exec("DROP TABLE IF EXISTS user");
$dbh->exec("CREATE TABLE user ( name VARCHAR(32), email 
VARCHAR(32), PRIMARY KEY (name) );");
$dbh->exec("INSERT INTO user VALUES 
('fritz', 'fritz@server.com')");
$dbh->exec("INSERT INTO user VALUES 
('otto', 'otto@server.com')");
		
// this will return 2 rows where 0 are expected
$stmt = $dbh->prepare("SELECT * FROM user WHERE name=:user 
OR email=:user");
$stmt->execute(array(':user' => 'franz'));
$rows = $stmt->fetchAll(PDO::FETCH_OBJ);
var_dump($rows);
		
// this workaround will return 0 rows as expected
$stmt = $dbh->prepare("SELECT * FROM user WHERE name=:user1 
OR email=:user2");
$stmt->execute(array(':user1' => 'franz', ':user2' 
=> 'franz'));
$rows = $stmt->fetchAll(PDO::FETCH_OBJ);
var_dump($rows);

Expected result:
----------------
array(0) { } array(0) { } 

Actual result:
--------------
array(2) { [0]=>  object(stdClass)#4 (2) { ["name"]=>  
string(5) "fritz" ["email"]=>  
string(16) "fritz@server.com" } [1]=>  object(stdClass)#5 
(2) { ["name"]=>  string(4) "otto" ["email"]=>  
string(15) "otto@server.com" } } array(0) { }

Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

This is a limitation of the MySQL prepared statement syntax 
which does not support re-usable identifiers. To make your 
query work you need to set PDO::ATTR_EMULATE_PREPARES to true.