Front matter URL/Permalink string contains `/` but is getting converted to `-`

[James Steinbach]

Post front matter is

---
title: Post Title
date: 2018-01-11
permalink: /post/title/
---

Metalsmith config is:

"metalsmith-permalinks": {
  "pattern": "/:permalink"
}

Desired behavior

Jekyll read this front matter & created /post/title/index.html. This is what I would like Metalsmith to do as well.

Actual behavior

The / in the permalink front matter property is converted to -. So this post ends up at /post-title/index.html.

Thanks in advance for your help!