diff --git a/apps/web/src/components/EditorPane.tsx b/apps/web/src/components/EditorPane.tsx
index 46a04202..cfc0e16c 100644
--- a/apps/web/src/components/EditorPane.tsx
+++ b/apps/web/src/components/EditorPane.tsx
@@ -1137,7 +1137,12 @@ const RichEditorPane = ({
         return true;
       },
     },
-  });
+  }, [
+    // A ProseMirror undo history belongs to exactly one memo. Reusing the same
+    // Editor instance across memo switches lets Ctrl/Cmd+Z undo the hydration
+    // transaction and restore another memo's entire document.
+    memo?.id,
+  ]);
 
   const insertMemoLink = useCallback((target: MemoSummary) => {
     if (!isEditorReady(editor) || effectiveReadOnly || target.id === memo?.id) {
diff --git a/tests/e2e/editor-undo-isolation.spec.ts b/tests/e2e/editor-undo-isolation.spec.ts
new file mode 100644
index 00000000..a248192d
--- /dev/null
+++ b/tests/e2e/editor-undo-isolation.spec.ts
@@ -0,0 +1,47 @@
+import { expect, test } from "@playwright/test";
+
+test("keeps undo history isolated when switching between search results", async ({ page }) => {
+  const marker = `undo-isolation-${Date.now()}`;
+  const notebooksResponse = await page.request.get("/api/v1/notebooks");
+  expect(notebooksResponse.ok()).toBe(true);
+  const notebooks = await notebooksResponse.json() as { notebooks: Array<{ id: string }> };
+  const notebookId = notebooks.notebooks[0]?.id;
+  expect(notebookId).toBeTruthy();
+
+  const createMemo = async (title: string, contentMarkdown: string) => {
+    const response = await page.request.post("/api/v1/memos", {
+      data: { notebookId, title, contentMarkdown },
+    });
+    expect(response.status()).toBe(201);
+    return (await response.json() as { memo: { id: string } }).memo;
+  };
+
+  const first = await createMemo(`${marker} first`, `${marker} FIRST CONTENT`);
+  const second = await createMemo(`${marker} second`, `${marker} SECOND CONTENT`);
+
+  try {
+    await page.goto("/");
+    await page.getByRole("button", { name: "全部笔记", exact: true }).click();
+    await page.getByPlaceholder("搜索笔记").fill(marker);
+
+    await page.locator(`[data-memo-id="${first.id}"]`).locator("button").first().click();
+    const editor = page.locator(".ProseMirror[contenteditable='true']");
+    await expect(editor).toContainText(`${marker} FIRST CONTENT`);
+
+    await page.locator(`[data-memo-id="${second.id}"]`).locator("button").first().click();
+    await expect(editor).toContainText(`${marker} SECOND CONTENT`);
+
+    await editor.click();
+    await page.keyboard.insertText(" accidental edit");
+    await page.keyboard.press("ControlOrMeta+z");
+
+    await expect(editor).toContainText(`${marker} SECOND CONTENT`);
+    await expect(editor).not.toContainText("accidental edit");
+    await expect(editor).not.toContainText(`${marker} FIRST CONTENT`);
+  } finally {
+    for (const memo of [first, second]) {
+      await page.request.delete(`/api/v1/memos/${memo.id}`);
+      await page.request.delete(`/api/v1/memos/${memo.id}?permanent=1`);
+    }
+  }
+});