src/java.base/share/classes/java/util/Formatter.java

@@ -2912,11 +2912,11 @@
                 break;
             case Conversion.LINE_SEPARATOR:
                 a.append(System.lineSeparator());
                 break;
             case Conversion.PERCENT_SIGN:
-                a.append('%');
+                print("%", l);
                 break;
             default:
                 assert false;
             }
         }