Strange boolean-discriminant narrowing with strictNullChecks off

TypeScript Version: nightly (2.1.0-dev.20160826)

Code

type Result = { success: true }
            | { success: false, error: string }

function handleError(res: Result) {
    if (res.success === true) {
        return;
    }

    res.error; // OK
}

function handleError2(res: Result) {
    if (res.success !== false) {
        return;
    }

    res.error; // OK
}

function handleError3(res: Result) {
    if (res.success) {
        return;
    }

    res.error; // Property 'error' does not exist on type 'Result'
               // but should be OK
}

Expected behavior: All three cases should behave the same.