Error calling supertrait method via trait reference

[jdm]

trait A {
    fn foo();
}

trait B: A {
}

struct BImpl {
    unused: int
}

impl BImpl: B {
}

impl BImpl: A {
    fn foo() {}
}

struct CImpl {
    b: B
}

impl CImpl: A {
    fn foo() {
        self.b.foo();
    }
}

fn main() {
    let b = BImpl { unused: 0 } as B;
    let c = CImpl { b: b };
    c.foo();
}

[jdm@rosencrantz traitinheritance]$ rustc test2.rs 
test2.rs:25:8: 25:21 error: type `@B` does not implement any method in scope named `foo`
test2.rs:25         self.b.foo();
                    ^~~~~~~~~~~~~

[jdm]

Here's a simpler testcase:

trait A {
    fn foo();
}

trait B: A {
}

impl int: A {
    fn foo() {}
}

impl int: B {
}

fn main() {
    5.foo();
    (5 as B).foo();
}

[jdm@rosencrantz traitinheritance]$ rustc test3.rs 
test3.rs:33:4: 33:19 error: type `@B` does not implement any method in scope named `foo`
test3.rs:33     (5 as B).foo();
                ^~~~~~~~~~~~~~~

[catamorphism]

Reproduced with 373504 but not critical for 0.6.

[jdm]

I guess this is the same as #4100.