title: UnsupportedTemporalTypeException: Unsupported field: InstantSeconds
body: <p>I have this code which is producing a timestamp and then parsing.</p>
  
  <pre><code>DateTimeFormatter formatter = 
      DateTimeFormatter
          .ofPattern("yyyyMMdd kk:HH:ss.SSSZ")
          .withLocale(Locale.getDefault())
          .withZone(ZoneId.systemDefault());
  
  Instant now = Instant.now();
  
  String formatted = formatter.format(now);
  Instant parsed = formatter.parse(formatted, Instant::from);
  </code></pre>
  
  <p>When it runs, the last line produces an exception:</p>
  
  <pre><code>java.time.format.DateTimeParseException: Text '20180123 12:12:45.648-0500' could not be parsed: Unable to obtain Instant from TemporalAccessor: {SecondOfMinute=45, NanoOfSecond=648000000, OffsetSeconds=-18000, MilliOfSecond=648, MicroOfSecond=648000, HourOfDay=12},ISO,America/New_York resolved to 2018-01-23 of type java.time.format.Parsed
  
  Caused by: java.time.DateTimeException: Unable to obtain Instant from TemporalAccessor: {SecondOfMinute=45, NanoOfSecond=648000000, OffsetSeconds=-18000, MilliOfSecond=648, MicroOfSecond=648000, HourOfDay=12},ISO,America/New_York resolved to 2018-01-23 of type java.time.format.Parsed
  
  Caused by: java.time.temporal.UnsupportedTemporalTypeException: **Unsupported field: InstantSeconds**
  </code></pre>
  
  <p>I replace the formatter with <strong>DateTimeFormatter.ISO_INSTANT</strong>, it works correctly. The actual data produced are nearly identical. What is the disconnect?</p>
  
  <pre><code>ISO_INSTANT:  2018-01-23T16:51:25.516Z
  My Format:    20180119 23:59:59.999-0800
  </code></pre>
  
  <p>I am required to use my format.  What is the problem here?</p>