FULL PRODUCT VERSION :
java version "1.8.0_77"
Java(TM) SE Runtime Environment (build 1.8.0_77-b03)
Java HotSpot(TM) 64-Bit Server VM (build 25.77-b03, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Mac OS 10.11.1

A DESCRIPTION OF THE PROBLEM :
The DateTimeFormatter fails to parse its own output for format strings containing "O". The following code throws a StringIndexOutOfBoundsException on the final line.

import java.time.ZoneOffset
import java.time.ZonedDateTime
import java.time.format.DateTimeFormatter
DateTimeFormatter formatter = DateTimeFormatter
        .ofPattern("yyyy-MM-dd'T'HH:mm:ss.S O")
        .withLocale(Locale.ENGLISH)
String date = formatter.format(ZonedDateTime.now(ZoneOffset.UTC));
formatter.parse(date)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
import java.time.ZoneOffset
import java.time.ZonedDateTime
import java.time.format.DateTimeFormatter
DateTimeFormatter formatter = DateTimeFormatter
        .ofPattern("yyyy-MM-dd'T'HH:mm:ss.S O")
        .withLocale(Locale.ENGLISH)
String date = formatter.format(ZonedDateTime.now(ZoneOffset.UTC));
formatter.parse(date)

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Successful parse
ACTUAL -
StringIndexOutOfBoundsException

ERROR MESSAGES/STACK TRACES THAT OCCUR :
java.time.format.DateTimeParseException: Text '2016-04-08T10:49:52.7 GMT' could not be parsed: String index out of range: 25

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.time.ZoneOffset
import java.time.ZonedDateTime
import java.time.format.DateTimeFormatter
DateTimeFormatter formatter = DateTimeFormatter
        .ofPattern("yyyy-MM-dd'T'HH:mm:ss.S O")
        .withLocale(Locale.ENGLISH)
String date = formatter.format(ZonedDateTime.now(ZoneOffset.UTC));
formatter.parse(date)
---------- END SOURCE ----------