FullCalendar header buttons missing
Having just had the same problem I suspect your issue is that you're missing the media="print" attribute on the fullcalendar.print.css style sheet link.
And if you're using Zend Framework to append the stylesheet, you can use this to add the media="print"...
$this->view->headLink()->appendStylesheet('/styles/jquery-plugins/fullcalendar.print.css', 'print');