rustc unused imports bug

unused_imports.rs

#[macro_use]
extern crate derive_more;
use std::ops::{Add, Sub, Div, Mul};

#[derive(Debug, Clone, Copy, Add, Mul)]
pub struct Vec3 {
    pub x: f64,
    pub y: f64,
    pub z: f64,
}

fn main() {}

// Errors on stable 1.20
warning: unused imports: `Div`, `Sub`
 --> src/main.rs:3:21
  |
3 | use std::ops::{Add, Sub, Div, Mul};
  |                     ^^^  ^^^
  |
  = note: #[warn(unused_imports)] on by default

warning: unused import: `Add`
 --> src/main.rs:3:16
  |
3 | use std::ops::{Add, Sub, Div, Mul};
  |                ^^^

warning: unused import: `Mul`
 --> src/main.rs:3:31
  |
3 | use std::ops::{Add, Sub, Div, Mul};
  |                               ^^^