A trivial generic interface extending a generic type handles assignability differently than the base type

[tjjfvi]

TypeScript Version: 4.0.5, 4.1.0-beta, 4.1.0-dev.20201102

Search Terms: generic interface assignability

Code

type Assert<T, U extends T> = U;

type A = { value: 5, a: true };
type B = { value: 5, b: true };

interface Box<T> {
    value: T;
}

type _Rebox<T extends Box<any>> = Box<T["value"]>;

namespace Test0 {
    type Rebox<T extends Box<any>> = _Rebox<T>;

    export type Assertions = [
        Assert<Box<5>, Rebox<A>>, // Correctly passes
        Assert<Rebox<A>, Box<5>>, // Correctly passes

        Assert<Box<5>, Rebox<B>>, // Correctly passes
        Assert<Rebox<B>, Box<5>>, // Correctly passes

        Assert<Rebox<A>, Rebox<B>>, // Correctly passes
    ];
}

namespace Test1 {
    interface Rebox<T extends Box<any>> extends _Rebox<T> {};

    export type Assertions = [
        Assert<Box<5>, Rebox<A>>, // Correctly passes
        Assert<Rebox<A>, Box<5>>, // Correctly passes

        Assert<Box<5>, Rebox<B>>, // Correctly passes
        Assert<Rebox<B>, Box<5>>, // Correctly passes

        Assert<Rebox<A>, Rebox<B>>, // Incorrectly fails
    ];
}

Expected behavior: Test0.Assertions and Test1.Assertions should both resolve with no errors.

Actual behavior: When Rebox is an interface (in Test1), Rebox<B> is not assignable to Rebox<A>.

Playground Link

Related Issues: N/A

[tjjfvi]

This also fails:

interface Rebox<T extends Box<any>> extends Box<T["value"]> {};