diff --git a/frontend/src/components/pageEditor/DragDropGrid.tsx b/frontend/src/components/pageEditor/DragDropGrid.tsx
index a13108079..6c7d1ec09 100644
--- a/frontend/src/components/pageEditor/DragDropGrid.tsx
+++ b/frontend/src/components/pageEditor/DragDropGrid.tsx
@@ -511,7 +511,7 @@ const DragDropGrid = <T extends DragDropItem>({
     const sourcePageNumber = activeData.pageNumber;
 
     const overData = over?.data.current;
-    const targetIndex = resolveTargetIndex(
+    let targetIndex = resolveTargetIndex(
       hoveredItemId,
       finalDropSide,
       visibleItems,
@@ -521,6 +521,8 @@ const DragDropGrid = <T extends DragDropItem>({
     );
 
     if (targetIndex === null) return;
+    if (targetIndex < 0) targetIndex = 0;
+    if (targetIndex > items.length) targetIndex = items.length;
 
     // Check if this page is box-selected
     const isBoxSelected = boxSelectedPageIds.includes(active.id as string);
diff --git a/frontend/src/components/pageEditor/PageEditor.tsx b/frontend/src/components/pageEditor/PageEditor.tsx
index 4b6afcfc7..9254f7342 100644
--- a/frontend/src/components/pageEditor/PageEditor.tsx
+++ b/frontend/src/components/pageEditor/PageEditor.tsx
@@ -200,6 +200,7 @@ const PageEditor = ({
         break;
       }
     }
+
     if (!hasAdditions && !hasRemovals) return;
 
     setEditedDocument(prev => {
@@ -213,22 +214,18 @@ const PageEditor = ({
 
       // Insert new pages while preserving current interleaving
       if (hasAdditions) {
-        // Insert file-by-file at the correct anchors
-        for (const [, additions] of newByFile) {
-          // Check if any page has insertAfterPageId (specific insertion point)
-          const hasSpecificInsertPoint = additions.some(p => (p as any).insertAfterPageId);
+        // Rebuild pages array respecting the order from mergedPdfDocument
+        // This handles file selection/deselection correctly (placeholder positioning)
+        const mergedOrder = mergedPdfDocument.pages.map(p => p.id);
+        const pageById = new Map(pages.map(p => [p.id, p]));
 
-          if (hasSpecificInsertPoint) {
-            // Insert after specific page (ignores file order)
-            const insertAfterPageId = (additions[0] as any).insertAfterPageId;
-            const insertAfterIndex = pages.findIndex(p => p.id === insertAfterPageId);
-            const insertAt = insertAfterIndex >= 0 ? insertAfterIndex + 1 : pages.length;
-            pages.splice(insertAt, 0, ...additions);
-          } else {
-            // Normal add: append to end
-            pages.push(...additions);
-          }
+        // Add new pages to the map
+        for (const [, additions] of newByFile) {
+          additions.forEach(p => pageById.set(p.id, p));
         }
+
+        // Rebuild in mergedPdfDocument order
+        pages = mergedOrder.map(id => pageById.get(id)!).filter(Boolean);
       }
 
       // Renumber without reordering
@@ -350,17 +347,28 @@ const PageEditor = ({
   }, [displayDocument, setSelectedPageIds, setSelectionMode]);
 
   // Automatically include newly added pages in the current selection
+  const previousPageIdsRef = useRef<Set<string>>(new Set());
   useEffect(() => {
-    if (!displayDocument || displayDocument.pages.length === 0) return;
+    if (!displayDocument || displayDocument.pages.length === 0) {
+      previousPageIdsRef.current = new Set();
+      return;
+    }
 
-    const currentSelection = new Set(selectedPageIds);
-    const newlyAddedPageIds = displayDocument.pages
-      .map(page => page.id)
-      .filter(pageId => !currentSelection.has(pageId));
+    const currentIds = new Set(displayDocument.pages.map(page => page.id));
+    const newlyAddedPageIds: string[] = [];
+    currentIds.forEach(id => {
+      if (!previousPageIdsRef.current.has(id)) {
+        newlyAddedPageIds.push(id);
+      }
+    });
 
     if (newlyAddedPageIds.length > 0) {
-      setSelectedPageIds([...selectedPageIds, ...newlyAddedPageIds]);
+      const next = new Set(selectedPageIds);
+      newlyAddedPageIds.forEach(id => next.add(id));
+      setSelectedPageIds(Array.from(next));
     }
+
+    previousPageIdsRef.current = currentIds;
   }, [displayDocument, selectedPageIds, setSelectedPageIds]);
 
   // DOM-first command handlers
diff --git a/frontend/src/components/pageEditor/PageThumbnail.tsx b/frontend/src/components/pageEditor/PageThumbnail.tsx
index fc7198696..5aadc2238 100644
--- a/frontend/src/components/pageEditor/PageThumbnail.tsx
+++ b/frontend/src/components/pageEditor/PageThumbnail.tsx
@@ -445,7 +445,7 @@ const PageThumbnail: React.FC<PageThumbnailProps> = ({
                 backgroundColor: 'white',
                 border: '1px solid #e9ecef',
                 borderRadius: 2
-              }}></div>
+              }} />
             </div>
           ) : thumbnailUrl ? (
             <img
diff --git a/frontend/src/components/pageEditor/hooks/usePageDocument.ts b/frontend/src/components/pageEditor/hooks/usePageDocument.ts
index 24970973c..eb6617e97 100644
--- a/frontend/src/components/pageEditor/hooks/usePageDocument.ts
+++ b/frontend/src/components/pageEditor/hooks/usePageDocument.ts
@@ -142,10 +142,21 @@ export function usePageDocument(): PageDocumentHook {
       return filePages;
     };
 
-    // Collect all pages from original files (without renumbering yet)
+    // Collect all pages from original files, respecting their previous positions
     const selectedFileIdsSet = new Set(state.ui.selectedFileIds);
+
+    // Sort original files by their position in fileOrder (so placeholders stay in correct spot)
+    // Use fileOrder as source of truth since it persists across page editor sessions
+    const fileOrderMap = new Map(allFileIds.map((id, index) => [id, index]));
+
+    const sortedOriginalFileIds = [...originalFileIds].sort((a, b) => {
+      const posA = fileOrderMap.get(a) ?? Number.MAX_SAFE_INTEGER;
+      const posB = fileOrderMap.get(b) ?? Number.MAX_SAFE_INTEGER;
+      return posA - posB;
+    });
+
     const originalFilePages: PDFPage[] = [];
-    originalFileIds.forEach(fileId => {
+    sortedOriginalFileIds.forEach(fileId => {
       const isSelected = selectedFileIdsSet.has(fileId);
       const filePages = createPagesFromFile(fileId, 1, isSelected); // Temporary numbering
       originalFilePages.push(...filePages);
@@ -184,6 +195,13 @@ export function usePageDocument(): PageDocumentHook {
       return null;
     }
 
+    // Pages are already in the correct order from the sorted assembly above
+    // Just ensure page numbers are sequential
+    pages = pages.map((page, index) => ({
+      ...page,
+      pageNumber: index + 1,
+    }));
+
     const mergedDoc: PDFDocument = {
       id: activeFileIds.join('-'),
       name,
@@ -193,7 +211,7 @@ export function usePageDocument(): PageDocumentHook {
     };
 
     return mergedDoc;
-  }, [activeFileIds, primaryFileId, primaryStirlingFileStub, processedFilePages, processedFileTotalPages, selectors, activeFilesSignature, selectedFileIdsKey, state.ui.selectedFileIds]);
+  }, [activeFileIds, primaryFileId, primaryStirlingFileStub, processedFilePages, processedFileTotalPages, selectors, activeFilesSignature, selectedFileIdsKey, state.ui.selectedFileIds, allFileIds]);
 
   // Large document detection for smart loading
   const isVeryLargeDocument = useMemo(() => {