Rust でコンパイルエラー

このプログラムを、ビルドすると所有権がらみのエラーになります。
エラーメッセージにある通りに、一旦、ローカル変数を経由して、２行に分けるだけで、解決してしまいます。。汗

なぜ？

fn main() {
    let mut h = Hoge { hoge2 : 0 }; 
    h.hoge3();
}

struct Hoge {
    hoge2:usize,
}

impl Hoge {
    fn get_byte(&mut self)->u8 { 0
    }
    fn format_byte(&mut self , address:u8 ) ->String {
        let s = format!("{:02X}H",address);
        s
    }
    
    fn hoge3(&mut self) {
        println!( "{}",format!("OR    {}",self.format_byte(self.get_byte() )));  // A

        //let a = self.get_byte();                                          // B
        //println!( "{}",format!("OR    {}",self.format_byte( a )));        // B
    }
    
}

⣿
Standard Error

   Compiling playground v0.0.1 (/playground)
error[E0499]: cannot borrow `*self` as mutable more than once at a time
  --> src/main.rs:19:60
   |
19 |         println!( "{}",format!("OR    {}",self.format_byte(self.get_byte() )));  // A
   |                                           -----------------^^^^^^^^^^^^^^^--
   |                                           |    |           |
   |                                           |    |           second mutable borrow occurs here
   |                                           |    first borrow later used by call
   |                                           first mutable borrow occurs here
   |
help: try adding a local storing this argument...
  --> src/main.rs:19:60
   |
19 |         println!( "{}",format!("OR    {}",self.format_byte(self.get_byte() )));  // A
   |                                                            ^^^^^^^^^^^^^^^
help: ...and then using that local as the argument to this call
  --> src/main.rs:19:43
   |
19 |         println!( "{}",format!("OR    {}",self.format_byte(self.get_byte() )));  // A
   |                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For more information about this error, try `rustc --explain E0499`.
error: could not compile `playground` due to previous error

Standard Output