diff --git a/lib/Controller/MappingsController.php b/lib/Controller/MappingsController.php
index 187960771..231633960 100644
--- a/lib/Controller/MappingsController.php
+++ b/lib/Controller/MappingsController.php
@@ -295,11 +295,26 @@ public function saveObject(): ?JSONResponse {
 			return new JSONResponse(['error' => $this->l->t('Missing required `object` field')], 400);
 		}
 
+		// 🔴 THE MAPPING RESULT MAY NOT ADDRESS AN EXISTING OBJECT.
+		//
+		// This endpoint saves the OUTPUT OF A MAPPING TEST as a new object —
+		// the UI button is "save result as object". A mapping transforms source
+		// data, and source data very often carries an `id`. `saveObject()`
+		// resolves its target from the payload (`@self.id` first, then `id`)
+		// and the write is PUT-semantic, so a result carrying either would
+		// silently REPLACE whatever object shares that identifier, nulling
+		// every field the result omitted, and report success.
+		//
+		// Identity here belongs to the new object, not to the source record the
+		// mapping happened to read.
+		$object = (array)$data['object'];
+		unset($object['id'], $object['uuid'], $object['@self']);
+
 		// OR's ObjectService::saveObject signature is `(object, register?,
 		// schema?)`. Prior code passed the register slug as the first arg
 		// — a TypeError under the new signature, which surfaced as 500.
 		$saved = $openRegisters->saveObject(
-			object:   $data['object'],
+			object:   $object,
 			register: ($data['register'] ?? 'openconnector'),
 			schema:   ($data['schema'] ?? 'mapping')
 		);
diff --git a/tests/Unit/Controller/MappingsControllerSaveObjectTest.php b/tests/Unit/Controller/MappingsControllerSaveObjectTest.php
new file mode 100644
index 000000000..5fe4fce5d
--- /dev/null
+++ b/tests/Unit/Controller/MappingsControllerSaveObjectTest.php
@@ -0,0 +1,128 @@
+<?php
+
+/**
+ * MappingsController::saveObject() identity test.
+ *
+ * The endpoint saves the OUTPUT OF A MAPPING TEST as an object — the UI button
+ * reads "save result as object". A mapping transforms SOURCE data, and source
+ * records very often carry an `id`.
+ *
+ * `ObjectService::saveObject()` resolves its target from the payload
+ * (`@self.id` first, then `id`) and the write is PUT-semantic, so a result
+ * carrying either would silently REPLACE whatever object shares that
+ * identifier, nulling every field the result omitted, and report success.
+ *
+ * @category Test
+ * @package  OCA\Integriq\Tests\Unit\Controller
+ *
+ * @author    Conduction Development Team <info@conduction.nl>
+ * @copyright 2026 Conduction B.V.
+ * @license   EUPL-1.2 https://joinup.ec.europa.eu/collection/eupl/eupl-text-eupl-12
+ *
+ * @link https://conduction.nl
+ *
+ * SPDX-FileCopyrightText: 2026 Conduction B.V. <info@conduction.nl>
+ * SPDX-License-Identifier: EUPL-1.2
+ */
+
+declare(strict_types=1);
+
+namespace OCA\Integriq\Tests\Unit\Controller;
+
+use OCA\Integriq\Controller\MappingsController;
+use OCA\Integriq\Service\ActionAuthService;
+use OCA\Integriq\Service\MappingService;
+use OCA\Integriq\Service\SourceMappingService;
+use OCA\OpenRegister\Db\ObjectEntity;
+use OCA\OpenRegister\Service\ObjectService;
+use OCP\IL10N;
+use OCP\IRequest;
+use OCP\IUserSession;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\LoggerInterface;
+
+/**
+ * A saved mapping result may not address an existing object.
+ */
+class MappingsControllerSaveObjectTest extends TestCase {
+	/**
+	 * The object handed to saveObject.
+	 *
+	 * @var array<string, mixed>|null
+	 */
+	private ?array $written = null;
+
+	/**
+	 * Build the controller over a request carrying the given body.
+	 *
+	 * @param array<string, mixed> $params The request parameters.
+	 *
+	 * @return MappingsController The controller.
+	 */
+	private function controller(array $params): MappingsController {
+		$request = $this->createMock(IRequest::class);
+		$request->method('getParams')->willReturn($params);
+
+		// The REAL ObjectService type (its test stub), because
+		// SourceMappingService::getOpenRegisters() declares that return type and
+		// an anonymous double is rejected outright. Mocking the declared type is
+		// also what keeps this honest: the assertion is about the argument the
+		// controller passes to the real signature.
+		$objectService = $this->createMock(ObjectService::class);
+		$objectService->method('saveObject')->willReturnCallback(
+			function ($object, ...$rest): ObjectEntity {
+				$this->written = (array)$object;
+
+				return new ObjectEntity();
+			}
+		);
+
+		$sourceMapping = $this->createMock(SourceMappingService::class);
+		$sourceMapping->method('getOpenRegisters')->willReturn($objectService);
+
+		$l = $this->createMock(IL10N::class);
+		$l->method('t')->willReturnArgument(0);
+
+		return new MappingsController(
+			'openconnector',
+			$request,
+			$this->createMock(MappingService::class),
+			$sourceMapping,
+			$l,
+			$this->createMock(IUserSession::class),
+			$this->createMock(ActionAuthService::class),
+			$this->createMock(LoggerInterface::class)
+		);
+	}//end controller()
+
+	/**
+	 * 🔴 A mapping result carrying an identity saves as a NEW object.
+	 *
+	 * The identity belongs to the source record the mapping read, not to the
+	 * object being created from it.
+	 *
+	 * @return void
+	 */
+	public function testAMappedIdentityDoesNotAddressAnExistingObject(): void {
+		$controller = $this->controller(
+			[
+				'object' => [
+					'id' => 'source-record-42',
+					'uuid' => 'source-record-42',
+					'@self' => ['id' => 'source-record-42'],
+					'title' => 'Mapped result',
+				],
+				'register' => 'zaken',
+				'schema' => 'zaak',
+			]
+		);
+
+		$controller->saveObject();
+
+		$this->assertIsArray($this->written, 'the save must have happened');
+		$this->assertArrayNotHasKey('id', $this->written);
+		$this->assertArrayNotHasKey('uuid', $this->written);
+		$this->assertArrayNotHasKey('@self', $this->written, '@self is read FIRST by saveObject');
+		$this->assertSame('Mapped result', $this->written['title'], 'the mapped payload still saves');
+	}//end testAMappedIdentityDoesNotAddressAnExistingObject()
+}//end class