Views Argument w/ Date field works as Page, not in Block summary

I have a content type ("Events") with a CCK-date field. I also have a view with an argument so that "/calendar/archive/200904" displays all the dates in April 2009. This same view has a block that, in the absence of an argument should default to "Summary, sorted ascending" with the option "summarize by month".

The page displays perfectly, but the block displays nothing (and, in fact, doesn't display at all since it has nothing to show). If I change the argument to be based on Node: Posted date instead of my CCK field then the block shows up (though obviously the data is a little wonky since the posted date has nothing do with the event date). So at least I know my view is fundamentally sound.

I have read through many other issues that look just like this and they all end with "This is fixed in the latest dev build [from last October]" but still I can't get it to work!

Any ideas? Thanks!

Important information:
Date module is 5.x-2.6
PHP is 5.2.9

Field definition is:

$content[fields]  = array (
  0 => 
  array (
    'widget_type' => 'date_popup',
    'label' => 'Date',
    'weight' => '-4',
    'default_value' => 'now',
    'default_value_code' => '',
    'default_value2' => 'blank',
    'default_value_code2' => '',
    'input_format' => 'Y-m-d H:i:s',
    'input_format_custom' => '',
    'year_range' => '-1:+3',
    'increment' => '15',
    'advanced' => 
    array (
      'label_position' => 'above',
      'text_parts' => 
      array (
        'year' => 0,
        'month' => 0,
        'day' => 0,
        'hour' => 0,
        'minute' => 0,
        'second' => 0,
      ),
    ),
    'description' => '',
    'group' => false,
    'required' => '1',
    'multiple' => '0',
    'repeat' => 0,
    'todate' => '',
    'granularity' => 
    array (
      'year' => 'year',
      'month' => 'month',
      'day' => 'day',
    ),
    'output_format_date' => 'l, F j, Y',
    'output_format_custom' => '',
    'output_format_date_long' => 'l, F j, Y - H:i',
    'output_format_custom_long' => '',
    'output_format_date_medium' => 'D, m/d/Y - H:i',
    'output_format_custom_medium' => '',
    'output_format_date_short' => 'm/d/Y - H:i',
    'output_format_custom_short' => '',
    'tz_handling' => 'none',
    'timezone_db' => '',
    'field_name' => 'field_date',
    'field_type' => 'date',
    'module' => 'date',
    'log' => '',
    'label_position' => 'above',
    'text_parts' => 
    array (
    ),
  ),
);

View export is:

  $view = new stdClass();
  $view->name = 'CalendarArchives';
  $view->description = 'Calendar Monthly Archive List';
  $view->access = array (
);
  $view->view_args_php = '';
  $view->page = TRUE;
  $view->page_title = '';
  $view->page_header = '';
  $view->page_header_format = '3';
  $view->page_footer = '';
  $view->page_footer_format = '3';
  $view->page_empty = '';
  $view->page_empty_format = '3';
  $view->page_type = 'node';
  $view->url = 'calendar/archive';
  $view->use_pager = TRUE;
  $view->nodes_per_page = '16';
  $view->block = TRUE;
  $view->block_title = 'Monthly Archive';
  $view->block_header = '';
  $view->block_header_format = '3';
  $view->block_footer = '';
  $view->block_footer_format = '3';
  $view->block_empty = '';
  $view->block_empty_format = '3';
  $view->block_type = 'node';
  $view->nodes_per_block = '25';
  $view->block_more = FALSE;
  $view->block_use_page_header = FALSE;
  $view->block_use_page_footer = FALSE;
  $view->block_use_page_empty = FALSE;
  $view->sort = array(
    array(
      'tablename' => 'node_data_field_date',
      'field' => 'field_date_value',
      'sortorder' => 'ASC',
      'options' => '',
    ),
  );
  $view->argument = array(
    array(
      'type' => 'content: field_date',
      'argdefault' => '4',
      'title' => '%1',
      'options' => 'month',
      'wildcard' => '',
      'wildcard_substitution' => '',
    ),
  );
  $view->field = array(
  );
  $view->filter = array(
    array(
      'tablename' => 'node',
      'field' => 'type',
      'operator' => 'OR',
      'options' => '',

      'value' => array (
  0 => 'event',
),
    ),
  );
  $view->exposed_filter = array(
  );
  $view->requires = array(node_data_field_date, node);
  $views[$view->name] = $view;