@@ -58,6 +58,7 @@ describe("on a scroll", () => {
   let left = 0;
   let top = 0;
   let scrolled = 0;
+  let scrolledDown = 0;
   let stripWidth = 1_000_000;
   let renders = 0;
 
@@ -108,11 +109,13 @@ describe("on a scroll", () => {
     left = 0;
     top = 0;
     scrolled = 0;
+    scrolledDown = 0;
     stripWidth = 1_000_000;
     renders = 0;
     host = document.body.appendChild(document.createElement("div"));
     host.setAttribute("data-timeline-scroll-viewport", "");
     Object.defineProperty(host, "scrollLeft", { configurable: true, get: () => scrolled });
+    Object.defineProperty(host, "scrollTop", { configurable: true, get: () => scrolledDown });
     root = harness.mount(host);
   });
 
@@ -145,6 +148,37 @@ describe("on a scroll", () => {
     expect(spans()).toEqual(["3072-5000"]);
   });
 
+  it("keeps a strip on screen measured after a move without a scroll, then a scroll", async () => {
+    await mountStrips(1);
+    expect(spans()).toEqual(["0-1536"]);
+
+    left = -3_000;
+    scrollTo(-1_000);
+    expect(spans()).toEqual(["0-2560"]);
+  });
+
+  it("measures a strip a vertical scroll brings on screen in that same frame", async () => {
+    neverReportedNear();
+    top = 5_000;
+    await mountStrips(1);
+    expect(spans()).toEqual(["0-0"]);
+
+    scrolledDown += 4_900;
+    top = 100;
+    act(() => host.dispatchEvent(new Event("scroll")));
+    act(() => frames.splice(0).forEach((frame) => frame(0)));
+
+    expect(spans()).toEqual(["0-1536"]);
+  });
+
+  it("keeps the tiles of a strip that ends just off screen", async () => {
+    await mountStrips(1);
+
+    scrollTo(-(stripWidth + 100));
+
+    expect(spans()).toEqual(["999424-1000000"]);
+  });
+
   it("measures the strips a jump brings on screen in that same frame", async () => {
     neverReportedNear();
     left = 50_000;
@@ -178,11 +212,11 @@ describe("on a scroll", () => {
   });
 
   it("keeps every tile of a short clip, even far from the screen", async () => {
-    stripWidth = 300;
+    stripWidth = 4_096;
     top = 5_000;
     await mountStrips(1);
 
-    expect(spans()).toEqual(["0-300"]);
+    expect(spans()).toEqual(["0-4096"]);
   });
 
   it("never re-measures a short clip on a scroll", async () => {
 
@@ -53,8 +53,8 @@ interface Strip {
 
 const NEAR_PX = IN_VIEW_CHUNK_PX / 2;
 
-// Each frame moves every strip's last box by the scroll since that box was read and reads only the
-// boxes that land near the screen, so a jump costs what a short scroll does; reads precede one commit.
+// Each frame reads the strips showing tiles, which a move without a scroll may have carried, and the
+// strips whose last box, moved by the scroll since, lands near the screen; reads precede one commit.
 const strips = new Map<Element, Strip>();
 let users = 0;
 let frame = 0;
@@ -112,8 +112,7 @@ const refresh = () => {
       width: box.width,
       height: box.height,
     };
-    if (isNear(moved)) updates.push([strip.apply, read(target, strip)]);
-    else if (strip.showing) updates.push([strip.apply, NOTHING_IN_VIEW]);
+    if (strip.showing || isNear(moved)) updates.push([strip.apply, read(target, strip)]);
   }
   commit(updates);
 };
 
@@ -0,0 +1,30 @@
+// @vitest-environment happy-dom
+import { act } from "react";
+import { expect, it } from "vitest";
+import { createHappyDomRootHarness } from "./testRootHarness";
+import { ThumbnailTiles } from "./ThumbnailTiles";
+
+Reflect.set(globalThis, "IS_REACT_ACT_ENVIRONMENT", true);
+
+const harness = createHappyDomRootHarness();
+
+it("places the first mounted tile where the full strip would have it", () => {
+  const host = document.body.appendChild(document.createElement("div"));
+  act(() =>
+    harness.mount(host).render(
+      <ThumbnailTiles
+        strip={{ width: 10_000, height: 40, inViewStart: 1_024, inViewEnd: 2_048 }}
+        frameW={100}
+        frameCount={100}
+        watchGap={() => {}}
+      >
+        {(index) => <i key={index} data-index={index} />}
+      </ThumbnailTiles>,
+    ),
+  );
+
+  const row = host.firstElementChild as HTMLElement;
+  const first = Number(row.querySelector("i")!.dataset.index);
+  expect(first).toBe(10);
+  expect(row.style.paddingLeft).toBe(`${first * 100}px`);
+});