Missing error for local interface merging with exported variable

[ajafff]

TypeScript Version: 2.4.0

Code

Noticed this in https://github.com/Microsoft/TypeScript/blob/master/src/harness/fourslash.ts#L4128

interface Foo { bar: number }
export namespace Foo {
    export let baz = 1;
}

same with variable instead of namespace

interface Foo { bar: number }
export var Foo = {
    baz: 1,
};

Expected behavior:
Individual declarations in merged declaration 'Foo' must be all exported or all local.

Actual behavior:
No error.

If I use a TypeAlias or class instead of the interface, it works as expected.