diff --git a/dicom-viewer/src/App.tsx b/dicom-viewer/src/App.tsx
index 11210cf..50fe66a 100644
--- a/dicom-viewer/src/App.tsx
+++ b/dicom-viewer/src/App.tsx
@@ -3189,29 +3189,37 @@ export default function App({ container_id, imageStacks, autoCacheStack, annotat
     name: string,
     requestedZone: ViewportDropZone,
   ) => {
-    const imageIds = await expandMultiframeImageIds(rawImageIds.map(normalizeToWadouriOrExternal));
+    const normalizedRawImageIds = dedupeImageIds(rawImageIds.map(normalizeToWadouriOrExternal));
+    if (normalizedRawImageIds.length === 0) return;
+
+    const existingStackIdx = availableStacks.findIndex((stackObj) => {
+      const existing = dedupeImageIds((stackObj.imageIds || []).map(normalizeToWadouriOrExternal));
+      return (
+        existing.length === normalizedRawImageIds.length
+        && existing.every((id, idx) => id === normalizedRawImageIds[idx])
+      );
+    });
+
+    if (existingStackIdx !== -1) {
+      // Reuse existing stack definitions whenever possible to avoid expensive
+      // expansion/probing and unnecessary network requests.
+      await applyStackDrop(viewportIdx, existingStackIdx, requestedZone);
+      setActiveViewport(viewportIdx);
+      return;
+    }
+
+    const imageIds = await expandMultiframeImageIds(normalizedRawImageIds);
     if (imageIds.length === 0) return;
     await setLoadedImageIdsAndCacheMeta(imageIds, { force: Boolean(autoCacheStack) });
     const seriesGroups = await deriveSeriesGroupsFromImageIds(imageIds);
     const primarySeries = seriesGroups[0]?.imageIds || imageIds;
 
-
-    // Check if a stack with the same imageIds already exists
-    let existingStackIdx = -1;
     let newStackIdx = -1;
     setAvailableStacks(prev => {
-      existingStackIdx = prev.findIndex(
-        s =>
-          s.imageIds.length === imageIds.length &&
-          s.imageIds.every((id, idx) => id === imageIds[idx])
-      );
-      if (existingStackIdx !== -1) {
-        return prev;
-      }
       newStackIdx = prev.length;
       return [...prev, { imageIds, name, seriesGroups, groupingSource: "derived" }];
     });
-    const stackIdxToUse = existingStackIdx !== -1 ? existingStackIdx : newStackIdx;
+    const stackIdxToUse = newStackIdx;
 
     const resolvedZone = resolveDropZone(requestedZone);
     if (resolvedZone === 'center') {
@@ -5583,6 +5591,26 @@ export default function App({ container_id, imageStacks, autoCacheStack, annotat
             </div>
           </div>
         )}
+        {loadingState === "displayset" && (
+          <div
+            style={{
+              position: "absolute",
+              inset: 0,
+              zIndex: 58,
+              pointerEvents: "none",
+              display: "flex",
+              alignItems: "center",
+              justifyContent: "center",
+              color: "rgba(255,255,255,0.78)",
+              fontSize: 14,
+              fontWeight: 600,
+              letterSpacing: 0.2,
+              textShadow: "0 1px 3px rgba(0,0,0,0.55)",
+            }}
+          >
+            Loading images...
+          </div>
+        )}
         <button
           style={{
             position: "absolute",
@@ -5736,6 +5764,42 @@ export default function App({ container_id, imageStacks, autoCacheStack, annotat
             </span>
           )}
         </button>
+        <button
+          style={{
+            position: "absolute",
+            top: 78,
+            left: 8,
+            zIndex: 20,
+            background: cineControlsOpenByViewport[i] ? "rgba(30,120,200,0.95)" : "#111",
+            color: "#fff",
+            border: "none",
+            borderRadius: "4px",
+            padding: "4px 8px",
+            cursor: "pointer",
+            fontSize: "16px",
+            lineHeight: 1,
+            opacity: 0.9,
+          }}
+          title={cineControlsOpenByViewport[i] ? "Hide cine controls" : "Show cine controls"}
+          onClick={(e) => {
+            e.stopPropagation();
+            setCineControlsOpenByViewport((prev) => {
+              const next = [...prev];
+              const nextOpen = !next[i];
+              next[i] = nextOpen;
+              if (!nextOpen) {
+                setCinePlayingByViewport((playing) => {
+                  const p = [...playing];
+                  p[i] = false;
+                  return p;
+                });
+              }
+              return next;
+            });
+          }}
+        >
+          <span aria-hidden="true">▶</span>
+        </button>
         {viewportModes[i] === "stack" && annotationNavEnabled && (() => {
           // Get all annotations for this stack
           const imageIds = viewportImageIds[i];
@@ -6003,38 +6067,6 @@ export default function App({ container_id, imageStacks, autoCacheStack, annotat
             gap: 6,
           }}
         >
-          <button
-            style={{
-              background: cineControlsOpenByViewport[i] ? "rgba(30,120,200,0.95)" : "rgba(0,0,0,0.7)",
-              color: "#fff",
-              border: "1px solid rgba(255,255,255,0.2)",
-              borderRadius: "4px",
-              fontSize: "12px",
-              fontWeight: 700,
-              padding: "6px 9px",
-              cursor: "pointer",
-              minHeight: 30,
-            }}
-            title={cineControlsOpenByViewport[i] ? "Hide cine controls" : "Show cine controls"}
-            onClick={(e) => {
-              e.stopPropagation();
-              setCineControlsOpenByViewport((prev) => {
-                const next = [...prev];
-                const nextOpen = !next[i];
-                next[i] = nextOpen;
-                if (!nextOpen) {
-                  setCinePlayingByViewport((playing) => {
-                    const p = [...playing];
-                    p[i] = false;
-                    return p;
-                  });
-                }
-                return next;
-              });
-            }}
-          >
-            Cine
-          </button>
           <div
             className="preset-menu"
             style={{
@@ -6716,7 +6748,7 @@ export default function App({ container_id, imageStacks, autoCacheStack, annotat
         overflow: "hidden",
       }}>
       {/* Loading overlay */}
-      {loadingState && (
+      {loadingState && loadingState !== "displayset" && (
         <div
           style={{
             position: "absolute",
@@ -6737,9 +6769,7 @@ export default function App({ container_id, imageStacks, autoCacheStack, annotat
         >
           {loadingState === "annotations"
             ? "Loading Annotations..."
-            : loadingState === "displayset"
-              ? "Loading Display Set..."
-              : "Loading Viewer State..."}
+            : "Loading Viewer State..."}
         </div>
       )}