This is weird. I tested this plugin on a test site with same WP version and same customized child theme and it worked fine.
When I use the plugin on the real site the author (class entry-author) is missing in the Print Friendly window.
The only differences between the sites are some css-stylings and a couple of plugins.
The site is http://www.abounderrattelser.fi/news/ and click on any article to test the print function.
Any help, any known plugins Print Friendly is conflicting with?