FormattableUtils.append re-parses literal output as format string

src/main/java/org/apache/commons/text/FormattableUtils.java

@@ -107,8 +107,7 @@ public static Formatter append(final CharSequence seq, final Formatter formatter
         for (int i = buf.length(); i < width; i++) {
             buf.insert(leftJustify ? i : 0, padChar);
         }
-        formatter.format(buf.toString());
-        return formatter;
+        return formatter.format(SIMPLEST_FORMAT, buf.toString());
     }
 
     /**

src/test/java/org/apache/commons/text/FormattableUtilsTest.java

@@ -144,6 +144,16 @@ void testIllegalEllipsisWith7Args() {
                 () -> FormattableUtils.append("foo", createFormatter(), 0, 0, precisionLessThanEllipsisLength, '}', ellipsis));
     }
 
+    @Test
+    void testPercentLiteral() {
+        assertEquals("100% done", FormattableUtils.append("100% done", new Formatter(), 0, -1, -1).toString());
+    }
+
+    @Test
+    void testPercentLiteralX2() {
+        assertEquals("50% off 100% items", FormattableUtils.append("50% off 100% items", new Formatter(), 0, -1, -1).toString());
+    }
+
     @Test
     void testPublicConstructorExists() {
         new FormattableUtils();