User-defined type guards seemingly unused when given an intersection type

[TyOverby]

TypeScript Version: 1.8.10

Code

interface Foo {
 x: number;
 s: string;
}

interface Bar {
 y: number;
 z: number;
}

interface HasNum {
 a: number;
}

type FooOrBar = Foo | Bar;

type FooOrBarWithNum = FooOrBar & HasNum;

function is_foo(f: FooOrBar): f is Foo {
 return (f as Foo).x !== undefined;
}

let obj: FooOrBarWithNum = {
 a: 5,
 x: 5,
 s: "hello"
};

if (is_foo(obj)) {
 obj.x; // ERROR: Property 'x' does not exist on type (Foo | Bar) & HasNum
}

let obj_2: FooOrBar = obj; // Cast it back to just a FooOrBar.

if (is_foo(obj_2)) {
 obj_2.x; // This compiles just fine.
}

Expected behavior:
I would expect obj to have type Foo inside of the if-block.

Actual behavior:
obj is not refined, but obj_2 is.

[yortus]

This looks related to or a duplicate of #9919

[yortus]

This works now. Fixed by #11717.