Generic of union type inferred as {}

[Arnavion]

(1.8.0-dev.20151201)

interface Foo<T> { prop: T; }

declare function lift<U>(value: U | Foo<U>): Foo<U>;

function unlift<U>(value: U | Foo<U>): U {
    return lift(value).prop; // error TS2322: Type '{}' is not assignable to type 'U'.
}

In 1.6 and 1.7 lift's generic is correctly inferred as U, so prop is of type U as expected. In 1.8 it's inferred as {}

Explicitly specifying the generic with lift<U>(value).prop works.