Please replace in common/responsive/default_attachment.php (and wherelse default_attachment is needed) the lines 38 and 39
$attribs = array('class'=>'file-name');
$attribs = array('class'=>'file-name','target'=>'_blank');
echo JHtml::_('link',str_replace(JPATH_SITE, "", JEMAttachment::getAttachmentPath($file->id)),$image,$attribs);
depebo has described it
for JEM 2.2x and it seems worth to be integrated into next update - since my PDF showed broken again after updating from JEM 2.2x to 2.3x.
depebo's solution obviously prevents pdf files from breaking and appearing distorted when they are downloaded from an event. Thx!