metadata override in README.md is being ignored

Ref: docs/metadata.md

I am working with XML in a README.md file that looks like this:
``` yaml
``` yaml
require:
- some/path/to/file.md

metadata:
authors: The Author I Want
```

The file `/some/path/to/file.md` contains the following:

```
> Values
``` yaml
metadata:
authors: Some other Author
```

I am finding that my attempt to override the `author` is being ignored - is this expected? Is there any way to make my override take affect?