Database logging in Zend Framework 2: wrong "extra" column name

I want to save log entries to my MySQL database from Zend Framework 2. I am using Zend\Log\Logger with a Zend\Log\Writer\Db writer. By supplying the writer with an array, one can choose which columns to save what data to (e.g. timestamp into a "log_date" column) and which data to save. Here is what I am doing:

$logger = new Zend\Log\Logger();

$mapping = array(
    'timestamp' => 'timestamp_column',
    'priority'  => 'priority_column',
    'message'   => 'message_column',
    'extra' => 'extra_column'
);

$logger->addWriter(new Zend\Log\Writer\Db($dbAdapter, 'table_name', $mapping));
$logger->err('some message', array('some extra information'));

The problem I am facing is that the array of column names and their values contain an incorrect column name for the "extra" column. Based on the array above, it should be inserting the value "some extra information" into the "extra_column" column. The problem is that the Zend\Log\Writer\Db class is using the letter "e" as the name of the extra column. This comes from the first letter of "extra_column" in my array above. For some reason, it is taking the first letter of "extra_column" and using it as the column name instead of the entire value.

I took a look at the source code. The mapEventIntoColumn method is being used to get the column names and values as an array. I copied in the relevant part of the method below.

// Example:
// $event = array('extra' => array(0 => 'some extra information'));
// $columnMap = array('extra' => 'extra_column');
// Return: array('e' => 'some extra information')
// Expected (without looking at the code below): array('extra_column' => 'some extra information')
protected function mapEventIntoColumn(array $event, array $columnMap = null) {
    $data = array();
    foreach ($event as $name => $value) {
        if (is_array($value)) {
            foreach ($value as $key => $subvalue) {
                if (isset($columnMap[$name][$key])) {
                    $data[$columnMap[$name][$key]] = $subvalue;
                }
            }
        }
    }
    return $data;
}

The $event parameter is an array containing the same keys as my $mapping array in my first code snippet and the values for the log message. The $columnMap parameter is the $mapping array from my first code snippet (array values are column names).

What actually seems to happen is that because I am passing in extra information as an array (this is required), the inner foreach loop is executed. Here, $key is 0 (the index) so it is actually doing like this: $columnMap['extra'][0]. This gives the letter "e" (the first letter in "extra_column"), which is used as the column name, where it should be the entire column name instead.

I tried to supply my own key in the extra array when calling the log method, but the same happens. The official documentation shows no examples of usage of the extra parameter. I want to insert information that can help me debug errors into my table, so I would like to use it.

Is this a bug or am I missing something? It seems really strange to me! I hope I explained it well enough - it is quite tricky!