Rust typing error?

gistfile1.rs

use std;
// uniq mut vec of mut f64
type umvomf64 = ~mutable [ mutable f64 ];

fn mk_umvomf64() -> umvomf64 {
  ret ~mutable [ mutable ];
}

fn main() {
  let cnt = 10u;
  let my_umvomf64 = [ vec::init_elt_mut(mk_umvomf64(), cnt) ];

  let my_stuff = mk_umvomf64();
  *my_stuff += [ mutable 1.03_f64 ];
  // test_type_error.rs:15:20: 15:28 error: mismatched types: expected `[mutable umvomf64]` but found `[umvomf64]` (types differ)
  // test_type_error.rs:15   my_umvomf64[2] <- [my_stuff];
                                               ^
  // rust: upcall fail 'explicit failure', ../src/comp/driver/session.rs:75
  my_umvomf64[2] <- [my_stuff];
}