Type guards doesn't work on multilevel if statements

I just noticed that type guards doesn't work on multilievel if statements? Is it by design?

``` typescript
var t: string | boolean | number;
if (typeof t === 'boolean' || typeof t === 'number') {
    if (typeof t === 'number') {        
    }
    else {
        t // should be boolean, but is string | boolean
    }
}
```
