diff --git a/packages/studio/src/player/components/timelineEditing.ts b/packages/studio/src/player/components/timelineEditing.ts
index c7293d90f..cba503c42 100644
--- a/packages/studio/src/player/components/timelineEditing.ts
+++ b/packages/studio/src/player/components/timelineEditing.ts
@@ -107,18 +107,16 @@ export function resolveTimelineMove(
     Math.max(0, input.maxStart),
   );
 
-  // Stacking mode: vertical movement writes z-index only. The authored
-  // data-track-index is preserved even when the pointer crosses rows.
+  // Stacking mode: the two axes never fight. Horizontal movement writes time
+  // (nextStart); vertical movement writes z-index. Lane/overlap resolution
+  // uses the clip's authored time span, NOT the dragged start — otherwise a
+  // diagonal drag that drifts the clip out of overlap silently flips the
+  // placement from "restack" to "join lane" and cancels the reorder.
   if (input.stackingElement) {
-    const stackingElement = {
-      ...input.stackingElement,
-      start: nextStart,
-      duration: input.duration,
-    };
     const layerMove =
       input.timelineLayers && input.layerOrder
         ? resolveTimelineLayerStackingMove({
-            element: stackingElement,
+            element: { ...input.stackingElement, duration: input.duration },
             layers: input.timelineLayers,
             layerOrder: input.layerOrder,
             trackDeltaRaw,
diff --git a/packages/studio/src/player/components/useTimelineClipDrag.test.tsx b/packages/studio/src/player/components/useTimelineClipDrag.test.tsx
index 0c71c0ffb..a90c598f3 100644
--- a/packages/studio/src/player/components/useTimelineClipDrag.test.tsx
+++ b/packages/studio/src/player/components/useTimelineClipDrag.test.tsx
@@ -202,13 +202,17 @@ describe("useTimelineClipDrag", () => {
     harness.unmount();
   });
 
-  it("uses the preview start when resolving whether a dragged clip can join a lane", async () => {
+  it("resolves lane stacking from the authored time span, independent of horizontal drag", async () => {
     const front = timelineElement({ id: "front", track: 0, zIndex: 3 });
     const back = timelineElement({ id: "back", track: 1, zIndex: 1 });
     back.start = 0;
     front.start = 0;
     const harness = renderDragHarness([front, back]);
 
+    // Drag up one row AND rightward in time. The horizontal drift moves the
+    // clip out of overlap, but the two axes never fight: the vertical restack
+    // is resolved from the authored (overlapping) span, so it still inserts
+    // above the target lane rather than silently joining it.
     harness.startDrag(back, 1);
     harness.movePointer(200, -TRACK_H);
     await harness.dropPointer();
@@ -219,8 +223,8 @@ describe("useTimelineClipDrag", () => {
       track: 1,
       stackingReorder: {
         contextKey: "root",
-        placement: { type: "onto", layerId: harness.layers[0]!.id },
-        zIndexChanges: [{ key: "back", zIndex: 3 }],
+        placement: { type: "above", layerId: harness.layers[0]!.id },
+        zIndexChanges: [{ key: "back", zIndex: 4 }],
       },
     });