diff --git a/packages/studio/src/player/components/timelineTrackOrder.test.ts b/packages/studio/src/player/components/timelineTrackOrder.test.ts
index e84cd431d..31d85c45e 100644
--- a/packages/studio/src/player/components/timelineTrackOrder.test.ts
+++ b/packages/studio/src/player/components/timelineTrackOrder.test.ts
@@ -34,16 +34,29 @@ function rowIds(rows: readonly { elements: readonly TimelineElement[] }[]): stri
 }
 
 describe("buildStackingTimelineLayers", () => {
-  it("packs non-overlapping clips into the same lane even when their z-index differs", () => {
+  it("splits non-overlapping clips into separate lanes when their z-index differs", () => {
+    // A lane is a z-band: differing z must land on different rows even when the
+    // clips don't overlap in time, so a vertical (z) restack actually moves the
+    // clip's row. Rows are ordered by descending z.
     const result = buildStackingTimelineLayers([
       rowElement({ id: "back", zIndex: 1, start: 0, duration: 1 }),
       rowElement({ id: "front", zIndex: 10, start: 1, duration: 1 }),
     ]);
 
-    expect(rowIds(result.visualLayers)).toEqual([["back", "front"]]);
+    expect(rowIds(result.visualLayers)).toEqual([["front"], ["back"]]);
     expect(result.visualLayers[0]?.zIndex).toBe(10);
   });
 
+  it("packs non-overlapping clips into one lane when they share a z-index", () => {
+    const result = buildStackingTimelineLayers([
+      rowElement({ id: "back", zIndex: 5, start: 0, duration: 1 }),
+      rowElement({ id: "front", zIndex: 5, start: 1, duration: 1 }),
+    ]);
+
+    expect(rowIds(result.visualLayers)).toEqual([["back", "front"]]);
+    expect(result.visualLayers[0]?.zIndex).toBe(5);
+  });
+
   it("splits clips into separate lanes when they overlap in time", () => {
     const result = buildStackingTimelineLayers([
       rowElement({ id: "front", zIndex: 10, start: 0, duration: 2 }),
diff --git a/packages/studio/src/player/components/timelineTrackOrder.ts b/packages/studio/src/player/components/timelineTrackOrder.ts
index 43e0014f3..4f3a41d7d 100644
--- a/packages/studio/src/player/components/timelineTrackOrder.ts
+++ b/packages/studio/src/player/components/timelineTrackOrder.ts
@@ -78,8 +78,13 @@ function getOrderedContextKeys(items: readonly TimelineLayerOrderItem[]): string
 }
 
 function canJoinLayer(layer: BuildLayer, item: TimelineLayerOrderItem): boolean {
+  // A row IS a z-band: clips only share a lane when they carry the same z-index
+  // (and don't overlap in time). Without the z-index gate a non-overlapping clip
+  // greedily packs into the first time-compatible row — the topmost one — so a
+  // vertical restack changes z but the row never follows it.
   return (
     layer.contextKey === resolveStackingContextKey(item) &&
+    layer.zIndex === item.zIndex &&
     layer.elements.every((element) => !timelineElementsOverlap(element, item.element))
   );
 }