Why property "does not exist" when do exist?

Using PHPUnit and building on Jenkins, this is the message that I got:

1) MyClassTest::testIsPropertyExist with data set #1 ('_table_usage') ReflectionException: Property _table_usage does not exist

When my test is:

/**
 * @dataProvider testIsPropertyExistDataProvider
 */
public function testReflectionClassIdtTransactionProperty($property)
{
    $object = new MyClass();
    $class = PHPUnitReflectionClass::getInstance($object);
    $response = $class->getProperty($property);
    $this->assertTrue(is_int($response) || is_bool($response));
}

public function testIsPropertyExistDataProvider() {
    return array(
        array('_idt'),
        array('_table_usage')
    );
}

And my class:

class MyClass
{
    private $_idt;
    private $_table_usage;

    public function __construct()
    {
        $this->_table_usage = false;
        $this->_idt = 1;
    }
}

So, i've been using the...

$class = PHPUnitReflectionClass::getInstance($object);
$response = $class->getProperty($property);

... in other tests, and having no problem.

So my doubts is, what am I missing and why the "_idt" exist?