I'm using standard Bootstrap 3 classes to style a modal. I'm having some issues with the alignment of a checkbox, and can't for the life of me figure out how to fix it.

Here's what it looks like when it's full-width:
![enter image description here](https://i.stack.imgur.com/9XnKJ.png)

The checkbox is not quite aligned center-vertical with the text, and it would be nice to fix, but that's not my main issue.

Here's what it looks like at a narrower view:
![enter image description here](https://i.stack.imgur.com/U7h4q.png)

At first I thought it was something in my code, like a style that was overriding Bootstrap, but I've copied my html into a [bootply](http://www.bootply.com/t0bKC0oEYu#) using nothing but standard bootstrap classes, and it behaves the same way.

My css is nothing to write home about; can anyone help me?