Setting a URL alias breaks the relative image paths on those pages. Is there a way to fix this?
src="sites/default/files/mobile-nav.png"> should be src="/sites/default/files/mobile-nav.png">

Please note the additional "/" before "sites." Without the forward slash the image will always be called from wherever you're at on the site so if you were at say site.com/news/ it would look for the images in site.com/news/sites/default.... if you don't have the forward slash before sites.