Union type is not determined with deep destructuring

[anvish]

TypeScript Version: 2.1.1 / nightly (2.2.0-dev.201xxxxx)
2.1.1
Code

type Option = 'a' | { result: number }

type Value = { option: Option }

function do1(value: Value) {
    if (value.option != 'a') {
        const { result } = value.option
    }
}

function do2(value: Value) {
    if (value.option != 'a') {
        const { option: { result } } = value // [ts] Type 'Option' has no property 'result' and no string index signature.
    }
}

Expected behavior:
do2 works as do1, type of value.option is determined
Actual behavior:
do2 works differently from do1, type of value.option is not determined

[ahejlsberg]

Duplicate of #10065 and #10846.