Index: src/wp-admin/includes/image.php
===================================================================
--- src/wp-admin/includes/image.php	(revision 36219)
+++ src/wp-admin/includes/image.php	(working copy)
@@ -408,6 +408,12 @@
 		}
 	}
 
+	foreach ( $meta['keywords'] as $key => $keyword ) {
+		if ( ! seems_utf8( $keyword ) ) {
+			$meta['keywords'][ $key ] = utf8_encode( $keyword );
+		}
+	}
+
 	foreach ( $meta as &$value ) {
 		if ( is_string( $value ) ) {
 			$value = wp_kses_post( $value );