Ticket #34981: 34981.3.diff

src/wp-includes/media.php

@@ -3139 +3139 @@
                 ) );
                 unset( $possible_sizes['full'] );
 
+                // The "thumbnail" size should always be set as it is used in the media modal and the media library
+                // to display the image thumbnails. If it is removed, they will end up using whatever size is available.
+                // For example they will load the full size images (which are far too large) if only they are available.
+                $possible_sizes = array_merge( array( 'thumbnail' => __('Thumbnail') ), $possible_sizes );
+
                 // Loop through all potential sizes that may be chosen. Try to do this with some efficiency.
                 // First: run the image_downsize filter. If it returns something, we can use its data.
                 // If the filter does not return something, then image_downsize() is just an expensive