Hi Rikard,
no I didn’t try 5.6.6 yet. The gallery.php looks quite the same on first sight.
I changed the following code to fix it (original lines 658–659):
$thumb_width = round( 100 / $atts['columns'], 4 );
$thumb_width = sprintf("%F",$thumb_width); // changes German decimal comma to decimal point
$element_styling->add_styles( 'thumb-link', array( 'width' => $thumb_width . '%' ) );
Kind regards,
Thorsten