diff --git a/src/State/TaskCalendarProcessor.php b/src/State/TaskCalendarProcessor.php
index fd612d4..5e3013e 100644
--- a/src/State/TaskCalendarProcessor.php
+++ b/src/State/TaskCalendarProcessor.php
@@ -8,6 +8,7 @@ use ApiPlatform\Metadata\Delete;
 use ApiPlatform\Metadata\Operation;
 use ApiPlatform\State\ProcessorInterface;
 use App\Entity\Task;
+use App\Entity\TaskStatus;
 use App\Service\CalDavService;
 use Doctrine\ORM\EntityManagerInterface;
 use Symfony\Component\DependencyInjection\Attribute\Autowire;
@@ -49,9 +50,16 @@ final readonly class TaskCalendarProcessor implements ProcessorInterface
             return $result;
         }
 
-        // CRITICAL: Store original status BEFORE persist to detect isFinal transition
-        $originalStatus  = $data->getStatus();
-        $wasAlreadyFinal = $originalStatus?->getIsFinal() ?? false;
+        // Detect isFinal transition using Doctrine UnitOfWork.
+        // $data already has the NEW values (API Platform deserialized the PATCH).
+        // UnitOfWork originalEntityData stores the DB snapshot with entity references for relations.
+        $uow             = $this->entityManager->getUnitOfWork();
+        $originalData    = $uow->getOriginalEntityData($data);
+        $wasAlreadyFinal = false;
+
+        if (isset($originalData['status']) && $originalData['status'] instanceof TaskStatus) {
+            $wasAlreadyFinal = $originalData['status']->getIsFinal();
+        }
 
         $result = $this->persistProcessor->process($data, $operation, $uriVariables, $context);