ADDITIONAL SYSTEM INFORMATION :
No additional configuration.

A DESCRIPTION OF THE PROBLEM :
The [`DateTimeFormatter` JavaDoc][1] explicitly states that when I use the `OOOO` pattern in my formatter, the **full form** of localized timezone should be used (emphasis mine):

> Four letters outputs the full form, which is localized offset text, such as 'GMT, **with 2-digit hour and minute field**, optional second field if non-zero, and colon, for example 'GMT+08:00'.

But in case the time is in GMT+0, the full form is not output, but instead just `GMT`.

Note: See the related [Stackoverflow question][2]

  [1]: https://docs.oracle.com/javase/8/docs/api/java/time/format/DateTimeFormatter.html
  [2]: https://stackoverflow.com/q/54875992/2237467


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Run the executable test case.
2. Observe the output string.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Wed 2019.02.27 15:55:38.177 GMT+00:00
ACTUAL -
Wed 2019.02.27 15:55:38.177 GMT

---------- BEGIN SOURCE ----------
package main;

import java.time.Instant;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;

public class Main {

    public static void main(String[] args) {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("EEE yyyy.MM.dd HH:mm:ss.SSS OOOO");
    
        String timestamp = OffsetDateTime.ofInstant(Instant.now(), ZoneOffset.UTC).format(formatter);
        System.out.println(timestamp);
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Using the timezone pattern `'GMT'xxxxx` instead of `OOOO`, which involves explicitly specifying the hard-coded substring `GMT` into the pattern.

FREQUENCY : always