framework: Strange behavior of emailOutputOnFailure() and runInBackground()

• Laravel Version: 5.8.23
• PHP Version: 7.2.16

Steps To Reproduce:

        $schedule
            ->command(Commands\ThrowsExceptionCommand::class)
            ->cron('* * * * *')
            ->description('foo')
            ->emailOutputOnFailure('foo@example.com')
        ;

        $schedule
            ->command(Commands\DoSomethingCommand::class)
            ->cron('* * * * *')
            ->description('bar')
            ->emailOutputOnFailure('bar@example.com')
        ;

        // This sends an email to foo@example.com with exception.
        // This is an correct behavior IMO.

        $schedule
            ->command(Commands\ThrowsExceptionCommand::class)
            ->cron('* * * * *')
            ->description('foo')
            ->emailOutputOnFailure('foo@example.com')
            ->runInBackground() // <- New Line
        ;

        $schedule
            ->command(Commands\DoSomethingCommand::class)
            ->cron('* * * * *')
            ->description('bar')
            ->emailOutputOnFailure('bar@example.com')
        ;

        // This works correctly too.

        $schedule
            ->command(Commands\ThrowsExceptionCommand::class)
            ->cron('* * * * *')
            ->description('foo')
            ->emailOutputOnFailure('foo@example.com')
        ;

        $schedule
            ->command(Commands\DoSomethingCommand::class)
            ->cron('* * * * *')
            ->description('bar')
            ->emailOutputOnFailure('bar@example.com')
            ->runInBackground() // <- New Line
        ;

        // Not only foo@example.com receives email with exception,
        // but also bar@example.com receives email with output of DoSomethingCommand.

        $schedule
            ->call(function () {echo 1;})
            ->cron('* * * * *')
            ->description('baz')
            ->emailOutputOnFailure('baz@example.com')
        ;

        // This ALWAYS sends an email to baz@example.com with empty body.

        $schedule
            ->call(function () {echo 1; throw new \Exception();})
            ->cron('* * * * *')
            ->description('baz')
            ->emailOutputOnFailure('baz@example.com')
        ;

        $schedule
            ->call(function () {echo 1; throw new \Exception();})
            ->cron('* * * * *')
            ->description('baz')
            ->emailOutputOnFailure('baz@example.com')
            ->runInBackground()
        ;

        // They work as same as the previous one.