Sorry, but your problem does not imply a bug in PHP itself.  For a
list of more appropriate places to ask for help using PHP, please
visit http://www.php.net/support.php as this bug system is not the
appropriate forum for asking support questions.  Due to the volume
of reports we can not explain in detail here why your report is not
a bug.  The support channels will be able to provide an explanation
for you.

Thank you for your interest in PHP.

Question marks are parameter placeholders.

The question mark is surrounded by quotes and so should be used as a literal value 
to query the table column, not as a parameter placeholder.  The exact same SQL 
statement executes fine when using PDO::query, e.g.

$result = $pdo->query("SELECT * FROM table WHERE column1 = '\' AND column2 = 
'?'");

The problem is also specific to the order in which the parameters appear in the 
statement, for instance this also executes without problem:

$stmt = $pdo->prepare("SELECT * FROM table WHERE column1 = '?' AND column2 = 
'\'");
$result = $stmt->execute();

So I assume the issue lies in the way PDO parses the SQL statement when preparing.