Porque én1_mut ainda é válido neste exemplo? Foi movido paraOption::Some então não deveria ser inválido?

struct MyRecordRec2<'a> {
    pub id: u32,
    pub name: &'a str,
    pub next: Box<Option<MyRecordRec2<'a>>>
}

#[test]
fn creating_circular_recursive_data_structure() {
    let mut n1_mut = MyRecordRec2 {
        id: 1,
        name: "n1",
        next: Box::new(None)
    };

    let n2 = MyRecordRec2 {
        id: 2,
        name: "n2",
        next: Box::new(Some(n1_mut))
    };

    //Why is n1_mut still valid?
    n1_mut.next = Box::new(Some(n2));
}

O seguinte não é compilado com o erro familiar "uso de valor movido":

#[test]
fn creating_and_freezing_circular_recursive_data_structure() {
    let loop_entry = {
        let mut n1_mut = MyRecordRec2 {
            id: 1,
            name: "n1",
            next: Box::new(None),
        };

        let n2 = MyRecordRec2 {
            id: 2,
            name: "n2",
            next: Box::new(Some(n1_mut)),
        };

        n1_mut.next = Box::new(Some(n2));

        n1_mut
    };
}

error[E0382]: use of moved value: `n1_mut`
  --> src/main.rs:44:9
   |
39 |             next: Box::new(Some(n1_mut)),
   |                                 ------ value moved here
...
44 |         n1_mut
   |         ^^^^^^ value used here after move
   |
   = note: move occurs because `n1_mut` has type `MyRecordRec2<'_>`, which does not implement the `Copy` trait