Model uniqueness validation doesn't work on update

I have a Uniqueness validator on a text field in my model. When I try to insert a new record with the same text as a previous record, the validations works and the new record does not get inserted. However, when I update an existing record with a text that is not unique, the validation does not seem to execute since the record gets updated with the non-unique text.

Am I doing something wrong here?

Sample code to reproduce:

<?php

$di = new Phalcon\DI\FactoryDefault();

$di->setShared('db', function () {
    return new \Phalcon\Db\Adapter\PDO\Sqlite(array(
        'dbname'   => ':memory:'
    ));
});

class Test extends \Phalcon\Mvc\Model
{
    public $mappedPrimaryKey;
    public $mappedData;

    public function columnMap()
    {
        // Keys are the real names in the table and
        // the values their names in the application
        //
        return array(
            "primaryKey"    => "mappedPrimaryKey",  
            "data"          => "mappedData"
        );
    }

    public function validation()
    {
        $validator = new Phalcon\Validation();          

            $validator->add( "mappedData",
                new Phalcon\Validation\Validator\Uniqueness( array(
                    "message" => "Data must be unique"
         )));

        return $this->validate( $validator );
    }
}

use \Phalcon\Db\Column as Column;

$di['db']->createTable(
    'test',
    null,
    [
       'columns' => [
            new Column(
                'primaryKey',
                [
                    'type'          => Column::TYPE_INTEGER,
                    'notNull'       => true,
                    'autoIncrement' => true,
                    'primary'       => true,
                ]
            ),
            new Column(
                'data',
                [
                    'type'    => Column::TYPE_TEXT,
                    'notNull' => true,
                ]
            )
        ]
    ]
);

$testObject1 = new Test;
$testObject1->mappedPrimaryKey = 1;
$testObject1->mappedData = "Object 1";

$testObject1->save();

$testObject2 = new Test;
$testObject2->mappedPrimaryKey = 2;
$testObject2->mappedData = "Object 2";

$testObject2->save();

$allRecords = Test::find();
foreach ( $allRecords as $record )
{
    echo $record->mappedPrimaryKey . ": " . $record->mappedData . "\n";
}
echo "\n";

$result = Test::findFirst( "mappedPrimaryKey = 1" );
$result->mappedData = "Object 2";   // Not unique
$result->save();

$allRecords = Test::find();
foreach ( $allRecords as $record )
{
    echo $record->mappedPrimaryKey . ": " . $record->mappedData . "\n";
}

echo "\nPhalcon Version: ", Phalcon\Version::get(), "\n";

My output:

1: Object 1
2: Object 2

1: Object 2
2: Object 2

Phalcon Version: 3.4.0