Index: wp-admin/includes/media.php
===================================================================
--- wp-admin/includes/media.php	(revision 32292)
+++ wp-admin/includes/media.php	(working copy)
@@ -861,10 +861,14 @@
 
 	// Finally check to make sure the file has been saved, then return the HTML.
 	if ( ! empty( $src ) ) {
-		if ( $return === 'src' ) {
+		if ( 'src' === $return ) {
 			return $src;
 		}
 
+		if ( 'id' === $return ) {
+			return $id;
+		}
+
 		$alt = isset( $desc ) ? esc_attr( $desc ) : '';
 		$html = "<img src='$src' alt='$alt' />";
 		return $html;
Index: wp-admin/includes/class-wp-press-this.php
===================================================================
--- wp-admin/includes/class-wp-press-this.php	(revision 32292)
+++ wp-admin/includes/class-wp-press-this.php	(working copy)
@@ -79,14 +79,38 @@
 					continue;
 				}
 
-				// Sideload image, which gives us a new image src.
-				$new_src = media_sideload_image( $image_src, $post_id, null, 'src' );
+				// Sideload image, which gives us a new image ID.
+				$image_id = media_sideload_image( $image_src, $post_id, null, 'id' );
 
-				if ( ! is_wp_error( $new_src ) ) {
+				if ( ! is_wp_error( $image_id ) ) {
+
+					$image_default_size = get_option('image_default_size');
+
+					// Get the image URI from the image ID, according to image_default_size option.
+					$src_array = wp_get_attachment_image_src( $image_id, $image_default_size );
+					$new_src = $src_array[0];
+					
+					// Make sure we got an image URI
+					if ( ! preg_match( '/[^\?]+\.(?:jpe?g|jpe|gif|png)(?:\?|$)/i', $new_src ) ) {
+						continue;
+					}
+
 					// Replace the POSTED content <img> with correct uploaded ones.
 					// Need to do it in two steps so we don't replace links to the original image if any.
 					$new_image = str_replace( $image_src, $new_src, $image );
 					$content = str_replace( $image, $new_image, $content );
+
+					// Replace the full image size class name with default image size class name,
+					// if specified.
+					if ( ! preg_match( '/(class=["\'][^"^\']+)["\']/', $image, $class_matches ) ) {
+						continue;
+					}
+					$class = $class_matches[1];
+					$new_class = $class;
+					if ( '' !== $image_default_size && 'full' !== $image_default_size ) {
+						$new_class = str_replace( 'size-full', 'size-' . $image_default_size, $class );
+					}
+					$content = str_replace( $class, $new_class, $content );
 				}
 			}
 		}