I added a new blog post to the example site after creating a /post folder. I moved the original example post there and all works well with config.rb set with:
blog.sources = "posts/{year}-{month}-{day}-{title}.html"
My new post is there:
The new YAML is:
---
title: "Getting Comfortable with Capture One Pro"
date: 2016-02-20
Tags: capture
---
Why doesn’t Middleman see and compile the new blog post?