Fix duplicate Locations appearing in map list

CHANGELOG.md

@@ -25,6 +25,7 @@ and this project somewhat adheres to [Semantic Versioning](https://semver.org/sp
 - Fix some menu items under `Tools` not being disabled when their corresponding button is disabled.
 - Fix the map list search bar stealing keyboard focus whenever a map layout was opened.
 - Disallow creating prefabs with no metatiles.
+- Fix new `Location` names created via the `Header` tab temporarily appearing twice after saving.
 
 ## [6.3.1] - 2026-04-12
 ### Added

src/ui/maplistmodels.cpp

@@ -128,16 +128,8 @@ QStandardItem *MapListModel::insertMapItem(const QString &mapName, const QString
         return nullptr;
 
     QStandardItem *map = createMapItem(mapName);
-
-    QStandardItem *folder = this->mapFolderItems[folderName];
-    if (!folder) {
-        // Folder doesn't exist yet, add it.
-        folder = insertMapFolderItem(folderName);
-    }
-    // If folder is still nullptr here it's because we failed to create it.
-    if (folder) {
-        folder->appendRow(map);
-    }
+    QStandardItem *folder = insertMapFolderItem(folderName);
+    if (folder) folder->appendRow(map);
     return map;
 }
 
@@ -145,6 +137,10 @@ QStandardItem *MapListModel::insertMapFolderItem(const QString &folderName) {
     if (folderName.isEmpty())
         return nullptr;
 
+    // If the folder has already been inserted, don't insert it again.
+    auto search = this->mapFolderItems.constFind(folderName);
+    if (search != this->mapFolderItems.constEnd()) return search.value();
+
     QStandardItem *item = createMapFolderItem(folderName);
     this->root->appendRow(item);
     return item;