Description:
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The test script below shows the point best.

One thing to notice, is that this bug only happens when you have 
standard_conforming_strings set to "on" in your postgres.conf file.

It seems like the fact that PHP uses '\' as escape char might be messing things 
up, sd $pdo->quote("\\") return '\' when standard_conforming_strings is set to 
"on" vs, '\\' when it's off.

Test script:
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$pdo = new PDO($dns, $username, $password);
$statement = $pdo->prepare("SELECT table.* FROM table table WHERE (column ILIKE :db_condition_placeholder_0 ESCAPE " . $pdo->quote("\\") . ") AND (column ILIKE :db_condition_placeholder_1 ESCAPE " . $pdo->quote("\\") . ");");
$statement->execute(array(':db_condition_placeholder_0' => 'test', ':db_condition_placeholder_1' => 'test'));

Expected result:
----------------
No errors and query executed:

Actual result:
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Error produced: Warning: PDOStatement::execute(): SQLSTATE[HY093]: Invalid 
parameter number: :db_condition_placeholder_1 in