Okay, so yes I just confirmed what you described. I will make edits accordingly.

PS - when I tried testing by changing:
```
redirect_from:
  - /writing/2013/markerboard-mentality/
  - /markerboard-mentality/
```
to
```
redirect_from:
  - /writing/2013/markerboard-mentality/
  - /markerboard-mentality
```
I got an error on the `jekyll build` generation:
```
$ jekyll build
Configuration file: /Users/joelglovier/code/github-jglovier/jglovier.github.io/_config.yml
            Source: /Users/joelglovier/code/github-jglovier/jglovier.github.io
       Destination: /Users/joelglovier/code/github-jglovier/jglovier.github.io/_site
      Generating... error: Is a directory - /Users/joelglovier/code/github-jglovier/jglovier.github.io/_site/markerboard-mentality. Use --trace to view backtrace
```
Apparently Jekyll didn't like that I was trying to replace a folder based redirect with a file based one?