Index: wp-includes/media-template.php
===================================================================
--- wp-includes/media-template.php	(wersja 40721)
+++ wp-includes/media-template.php	(kopia robocza)
@@ -773,7 +773,9 @@
 				) );
 
 				foreach ( $size_names as $size => $label ) : ?>
-					<option value="<?php echo esc_attr( $size ); ?>">
+					<option value="<?php echo esc_attr( $size ); ?>" <#
+						if ( '<?php echo $size ?>' == wp.media.galleryDefaults.size ) { #>selected="selected"<# }
+									#>>
 						<?php echo esc_html( $label ); ?>
 					</option>
 				<?php endforeach; ?>