Issue when returning a struct from an interface method

Consider this example program:

use serde::{Deserialize, Serialize};
use zbus::{blocking::Connection, dbus_interface};
use zvariant::derive::Type;

#[derive(Deserialize, Serialize, Type)]
struct MyStruct {
    value1: String,
    value2: String,
}

struct MyIface;

#[dbus_interface(name = "org.zbus.MyIface")]
impl MyIface {
    fn get_struct(&self) -> MyStruct {
        MyStruct {
            value1: "One".into(),
            value2: "Two".into()
        }
    }
}

fn main() {
    let conn = Connection::session().unwrap();
    conn.request_name("org.zbus.Test").unwrap();
    conn.object_server_mut().at("/org/zbus/test", MyIface).unwrap();
    loop {}
}

Calling this server like so:

busctl --user call org.zbus.Test /org/zbus/test org.zbus.MyIface GetStruct

Results in this reply:

ss "One" "Two"

Which I think is a bug. Here is the introspection data:

busctl --user introspect org.zbus.Test /org/zbus/test org.zbus.MyIface
NAME             TYPE      SIGNATURE RESULT/VALUE FLAGS
.GetStruct       method    -         (ss)         -

A struct should clearly be returned. To achieve proper behavior, I have to modify the method like this:

fn get_struct(&self) -> (MyStruct,) {
    (MyStruct {
        value1: "One".into(),
        value2: "Two".into()
    },)
}

Which is ugly and shouldn't be necessary according to the documentation.