Safari increases letter-spacing when using text-shadow

Question

Here's an example of the CSS that's giving me grief:

@import 'https://fonts.googleapis.com/css?family=Pathway+Gothic+One';

body {
  background: #444444;
}

h1 {
  font-family: 'Pathway Gothic One';
  text-transform: uppercase;
  color: #DD0000;
  letter-spacing: 0;
  text-shadow: 1px 1px 1px black;
}

<h1>Breaking News</h1>

In Chrome, it looks correct, but in Safari it increases the letter-spacing by 1 pixel.

Chrome screenshot

Safari screenshot

To prove this, if I change to letter-spacing: -1px, Safari looks fine, but Chrome looks too squashed.