Assignment to intersection type failing to check property type

[zamb3zi]

TypeScript Version: 2.1.5

Code

type A1 = {
    foo: number,
};
type B1 = A1 & {
    bar: {x: boolean}
};
const b1: B1 = {
    foo: 5,
    bar: {x: true, zoo: 5} // OK but expected: "'zoo' does not exist on type '{x: boolean}'"
}
b1.bar.zoo = 5; // Error as expected: "'zoo' does not exist on type '{x: boolean}'"
b1.bar = {x: true, zoo: 5}; // Error as expected: "'zoo' does not exist on type '{x: boolean}'"

type A2 = {
    foo: number,
    bar: {x: boolean} // this is the only difference from case 1 (type intersection is avoided)
};
const a2: A2 = {
    foo: 5,
    bar: {x: true, zoo: 5} // Error as expected: "'zoo' does not exist on type '{x: boolean}'"
}

Expected behavior:

When assigning to an intersection type, the types of the merged properties should be checked as if they were being assigned individually.

Actual behavior:

Type errors are missed, as described.

[zamb3zi]

My workaround was to use classes instead. This works:

class C1 {
    foo: number;
}
class C2 extends C1 {
    bar: {x: boolean}
}
const c2: C2 = {
    foo: 5,
    bar: {x: true, zoo: 5} // Error as expected: "'zoo' does not exist on type '{x: boolean}'"
};

[sktw]

I raised an issue about this yesterday #13813. Interesting that individual assignment errors are handled as expected.