[NLL] Incorrect lifetimes infered with pattern

[matthewjasper]

Minified from https://www.reddit.com/r/rust/comments/7lq5t3/featurenll_available_in_nightly/droaz2o/

This incorrectly compiles:

#![feature(nll)]

fn foo(s: &mut (i32,)) -> i32 {
    let &mut (ref x,) = &mut *s; // or {s}
    *s = (2,);
    *x    // 2, which is clearly incorrect
}

These variations correctly error:

fn foo(s: &mut (i32,)) -> i32 {
    let (ref x,) = *s;
    *s = (2,);
    *x
}

fn foo(s: &mut (i32,)) -> i32 {
    let x = &{&mut *s}.0;
    *s = (2,);
    *x
}

fn foo(s: &mut i32) -> i32 {
    let &mut ref x = &mut *s;
    *s = 2;
    *x
}

[arielb1]

And without patterns:

#![feature(nll)]

fn foo(s: &mut (i32,)) -> i32 {
    let t = &mut *s;
    let x = &t.0; // or {s}
    *s = (2,);
    *x    // 2, which is clearly incorrect
}

Why is this broken?