Why Are All My List Items Being Wrapped In SPAN Tags Automatically?

I was editing a page and typed out a list of items that I converted into an unordered list. However, when I switched over from Visual to Text view in the editor, I noticed all of my list items had extra SPAN tags wrapped around them, with a specific Font Size and Line Height declared for each. Is this normal for WordPress to do this? If so, is there a way to disable this? I disabled all of my plugins and switched back to the Twenty Twelve theme and I am still having this issue. Below is a sample of what the code looks like:

<ul>
	<li><span style="line-height: 1.714285714; font-size: 1rem;">Link one</span></li>
	<li><span style="line-height: 1.714285714; font-size: 1rem;">Link two</span></li>
	<li><span style="line-height: 1.714285714; font-size: 1rem;">Link three</span></li>
</ul>