diff --git a/backend/main.py b/backend/main.py
index 5e770ff..ec4ab70 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -398,20 +398,6 @@ async def delete_list(
     item = await _owned_list(db, user.id, list_id)
     if item.is_inbox:
         raise HTTPException(status_code=409, detail="系统收集箱不能删除")
-    inbox_id = await db.scalar(
-        select(TaskList.id).where(
-            TaskList.user_id == user.id,
-            TaskList.is_inbox.is_(True),
-            TaskList.deleted_at.is_(None),
-        )
-    )
-    if inbox_id is None:
-        raise HTTPException(status_code=409, detail="系统收集箱不存在")
-    await db.execute(
-        update(Task)
-        .where(Task.user_id == user.id, Task.list_id == item.id, Task.deleted_at.is_(None))
-        .values(list_id=inbox_id, version=Task.version + 1, updated_at=utcnow())
-    )
     item.deleted_at = utcnow()
     await db.commit()
     return Response(status_code=204)
@@ -507,7 +493,16 @@ async def list_tasks(
     db: AsyncSession = Depends(get_db),
 ):
     query = select(Task).where(
-        Task.user_id == user.id, Task.deleted_at.is_(None), Task.parent_id.is_(None)
+        Task.user_id == user.id,
+        Task.deleted_at.is_(None),
+        Task.parent_id.is_(None),
+        exists(
+            select(TaskList.id).where(
+                TaskList.id == Task.list_id,
+                TaskList.user_id == user.id,
+                TaskList.deleted_at.is_(None),
+            )
+        ),
     )
     if list_id is not None:
         await _owned_list(db, user.id, list_id)
@@ -617,7 +612,15 @@ async def get_task(
     db: AsyncSession = Depends(get_db),
 ):
     task = await db.scalar(
-        select(Task).where(Task.id == task_id, Task.user_id == user.id, Task.deleted_at.is_(None))
+        select(Task)
+        .join(TaskList, TaskList.id == Task.list_id)
+        .where(
+            Task.id == task_id,
+            Task.user_id == user.id,
+            Task.deleted_at.is_(None),
+            TaskList.user_id == user.id,
+            TaskList.deleted_at.is_(None),
+        )
     )
     if task is None:
         raise HTTPException(status_code=404, detail="任务不存在")
diff --git a/tests/test_app.py b/tests/test_app.py
index db1bbcd..a9dbfc2 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -314,15 +314,25 @@ def test_inbox_is_protected_and_deleted_collections_are_hidden(client):
     task = client.post(
         "/api/v1/tasks", json={"title": "保留任务", "list_id": task_list["id"]}
     ).json()
+    completed_task = client.post(
+        "/api/v1/tasks", json={"title": "已完成任务", "list_id": task_list["id"]}
+    ).json()
+    completed_task = client.patch(
+        f"/api/v1/tasks/{completed_task['id']}",
+        json={"completed": True, "version": completed_task["version"]},
+    ).json()
     assert client.delete(f"/api/v1/lists/{task_list['id']}").status_code == 204
     assert all(row["id"] != task_list["id"] for row in client.get("/api/v1/lists").json())
+    assert client.get("/api/v1/tasks", params={"q": "保留任务"}).json()["items"] == []
+    assert client.get(f"/api/v1/tasks/{task['id']}").status_code == 404
     archived = client.get("/api/v1/lists", params={"archived": True})
     assert archived.status_code == 200
     assert [row["id"] for row in archived.json()] == [task_list["id"]]
     assert client.post(f"/api/v1/lists/{task_list['id']}/restore").status_code == 200
     assert any(row["id"] == task_list["id"] for row in client.get("/api/v1/lists").json())
-    moved = client.get(f"/api/v1/tasks/{task['id']}").json()
-    assert moved["list_id"] == inbox["id"]
+    restored = client.get("/api/v1/tasks", params={"list_id": task_list["id"]}).json()["items"]
+    assert [row["id"] for row in restored] == [task["id"], completed_task["id"]]
+    assert restored[1]["completed"] is True
     assert client.delete(f"/api/v1/folders/{folder['id']}").status_code == 204
     assert client.get("/api/v1/folders").json() == []