The plugin also tries to shorten the canonical tag (e.g. inserted with plugins like WP SEO), which results in a wrong canonical syntax.
Without "Absolute-to-Relative URLs" the tag looks like
<link rel="canonical" href="http://www.nameofwebsite.com/post_slug/" />
when enabling the plugin and also the plugin wp-minify this tag is destroyed into
<link rel="canonical" href="./" />