Compiler incorrectly warns that a variable "does not need to be mutable"

[canndrew]

The following code:

#![feature(unboxed_closures)]

fn main() {
  let mut zarp: Vec<int> = Vec::new();
  let cls = move |&mut:| {
    zarp.push(3);
  };
}

Generates the following warning:

warning: variable does not need to be mutable, #[warn(unused_mut)] on by default
let mut zarp: Vec<int> = Vec::new();

However if I remove the mut from zarp it fails to compile (as it should).

[bkoropoff]

I thought I fixed this, but I guess I missed a case.