`as`, impls, and autounboxing, used together, segfault

[paulstansifer]

type t = { a: int };

iface it {
    fn f();
}

impl  of it for t {
    fn f() { }
}

fn main() {
    let x = ({a: 4i} as it);
    let y = @({a: 4i});
    let z = @({a: 4i} as it);
    x.f();
    y.f();
    (*z).f();
    #error["ok so far..."];
    z.f(); //segfault
}