Merge magento-partners/magento2ce#8.

Author: Volodymyr Kublytskyi

app/code/Magento/Catalog/Model/Category.php

@@ -1094,7 +1094,11 @@ public function reindex()
         if ($this->flatState->isFlatEnabled()) {
             $flatIndexer = $this->indexerRegistry->get(Indexer\Category\Flat\State::INDEXER_ID);
             if (!$flatIndexer->isScheduled()) {
-                $flatIndexer->reindexRow($this->getId());
+                $idsList = [$this->getId()];
+                if ($this->dataHasChangedFor('url_key')) {
+                    $idsList = array_merge($idsList, explode(',', $this->getAllChildren()));
+                }
+                $flatIndexer->reindexList($idsList);
             }
         }
         $productIndexer = $this->indexerRegistry->get(Indexer\Category\Product::INDEXER_ID);

app/code/Magento/Catalog/Test/Unit/Model/CategoryTest.php

@@ -318,7 +318,7 @@ public function testReindexFlatEnabled($flatScheduled, $productScheduled, $expec
             ->will($this->returnValue(true));
 
         $this->flatIndexer->expects($this->exactly(1))->method('isScheduled')->will($this->returnValue($flatScheduled));
-        $this->flatIndexer->expects($this->exactly($expectedFlatReindexCalls))->method('reindexRow')->with('123');
+        $this->flatIndexer->expects($this->exactly($expectedFlatReindexCalls))->method('reindexList')->with(['123']);
 
         $this->productIndexer->expects($this->exactly(1))->method('isScheduled')->will($this->returnValue($productScheduled));
         $this->productIndexer->expects($this->exactly($expectedProductReindexCall))->method('reindexList')->with($pathIds);