ADDITIONAL SYSTEM INFORMATION :
Microsoft Windows [Version 10.0.17134.320]

openjdk version "11" 2018-09-25
OpenJDK Runtime Environment 18.9 (build 11+28)
OpenJDK 64-Bit Server VM 18.9 (build 11+28, mixed mode)

openjdk version "12-ea" 2019-03-19
OpenJDK Runtime Environment 19.3 (build 12-ea+13)
OpenJDK 64-Bit Server VM 19.3 (build 12-ea+13, mixed mode)

A DESCRIPTION OF THE PROBLEM :
Running the attached testcase under Java 10.0.2 works. Running the same testcase under Java 11 or Java 12 throws a DateTimeParseException.

REGRESSION : Last worked in version 10.0.2

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run testcase

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Result: 2018-09-29T20:49:02Z
ACTUAL -
Exception in thread "main" java.time.format.DateTimeParseException: Text 'Sat, 29 Sep 2018 20:49:02 GMT' could not be parsed at index 0
        at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:2046)
        at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1948)
        at Testcase.main(Testcase.java:14)

---------- BEGIN SOURCE ----------
import java.time.Instant;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.time.format.DateTimeFormatterBuilder;
import java.util.Locale;

class Testcase
{
	public static void main (String[] args) throws java.lang.Exception
	{
		DateTimeFormatter dateFormatter = new DateTimeFormatterBuilder().
		  appendPattern("EEE, dd MMM yyyy HH:mm:ss zzz").
		  toFormatter(Locale.CANADA);
		Instant result = dateFormatter.parse("Sat, 29 Sep 2018 20:49:02 GMT", Instant::from);
		System.out.println("Result: " + result);
	}
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Use Locale.US instead of Locale.CANADA

FREQUENCY : always