Monolog rotating log not formatted correctly

Question

Using monolog (3.2) with rotating logs handler. Everything works fine BUT, the rotated logs don't use the log format I set. The main log is fine; the dated logs use the default output format instead.

It looks like the RotatingFileHandler should inherit format from parent, but for some reason it isn't. I'm mystified.

    $log = $dir . '/today.log';
    $outputFormat = "[%datetime%] %level_name% > %message% %context% %extra%\n";

        $dateFormat = 'Y-m-d H:i';
        $line_format = new LineFormatter($outputFormat, $dateFormat);
        $stream = new StreamHandler($log, Level::Debug);
        $stream->setFormatter($line_format);
        //  u\echor($stream,'stream',STOP);
        $logger -> pushHandler($stream);

        $fileHandler = new RotatingFileHandler($log,5);
        $logger->pushHandler($fileHandler);
...