Indented code blocks lose their formatting (0.13.19)

Create a code block, e.g:

```js
function main() {
  return 'test';
}
```

See how it’s rendered :

Now indent this block using Tab key:

    ```js
    function main() {
      return 'test';
    }
    ```

Now it gets rendered like an inline code, without code highlighting, with back-ticks visible:

Using the default theme.

Here is a Gist where everything works correctly:

This is not a bug.
it’s not rendered as an inline code. It’s rendered as a code block INCLUDING the first and last line.

But why it’s correct. On GitHub it works differently, and GitHub is the main application of Markdown in this world. Shouldn’t we follow the way it works?