default_type_params inference failure

infe.rs

#![feature(default_type_params)]

enum Enum<L = (), R = ()> {
    Both(L, R),
    Left(L),
    Right(R),
}

fn main() {
    // I'm expecting the compiler to choose the type `Enum<u8, ()>` here
    let left = Enum::Left(0u8);
    //^~ error: unable to infer enough type information about `Enum<u8, _>`; type annotations required
    // and the type `Enum<(), u8>` here, because `Enum` has default type parameters
    let right = Enum::Right(0u8);
    //^~ error: unable to infer enough type information about `Enum<_>`; type annotations required

    // But instead, I need to hint the default type parameters...
    let left: Enum<_, ()> = Enum::Left(0u8);  // OK
    let right: Enum<(), _> = Enum::Right(0u8);  // OK
}