Github user greghogan commented on the pull request: https://github.com/apache/flink/pull/1464#issuecomment-165499126 I haven't found a prohibition on returning the second input to a user-defined reduce function. I think fixing this in code is preferable to documenting the problem or throwing an error, especially since the problem only exists with object reuse enabled. Object reuse is configured in JavaProgramTestBase but must be set in the ExecutionEnvironmentFactory by TestEnvironment. I don't see that any of the many tests subclassing JavaProgramTestBase were testing with object reuse enabled. It is rather difficult to test for object reuse. ObjectReuseITCase simply captured a few isolated instances of strange behavior (with the original tests 3 and 4 being perfect copies). I would look to duplicate the first two tests in the appropriate JavaProgramTestBase subclass and delete ObjectReuseITCase.
--- If your project is set up for it, you can reply to this email and have your reply appear on GitHub as well. If your project does not have this feature enabled and wishes so, or if the feature is enabled but not working, please contact infrastructure at infrastruct...@apache.org or file a JIRA ticket with INFRA. ---