Why does bootstrap add an extra horizontal line?

http://codepen.io/juanmndz/full/ygdzMg/ Whenever, I switched to mobile I get this line near the bottommy horizontal element that I did. It looks like every .container-fluid a horizontal line is added but don’t know why. So it would show as two lines picture here:

Any help explaining why this is happening and how to fix this to just show one white horizontal line would greatly appreciated.
Note: The problem seems to be showing just for mobile.

because, at the bottom of every paragraph you have this <hr/> tag.


It’s actually very strange that you can’t see it on your non-mobile device. I can see it on my desktop. The <hr> tag adds a line. That’s what it does.