"date_timezone_set() expects parameter 1 to be DateTime" warning with Views using day argument

Full error: Warning: date_timezone_set() expects parameter 1 to be DateTime, boolean given in format_date() (line 1893 of [...]/includes/common.inc).

Reproduce as follows:
Create a page View that uses the day of month in the view argument, set it display a summary if no arguments given
Go to page URL and do not give it an argument

Sample view attached.

The problem is in the views_date_sql_format() function. For mysql/mysqli, the 'd' tolken is being converted to %%d instead of %d. This causes an invalid date string to be passed to the format_date() function.

<?php 
function views_date_sql_format($format, $field, $field_type = 'int', $set_offset = NULL) {
  $db_type = db_driver();
  $field = views_date_sql_field($field, $field_type, $set_offset);
  switch ($db_type) {
    case 'mysql':
    case 'mysqli':
      $replace = array(
        'Y' => '%Y',
        'm' => '%m',
        'd' => '%%d',
        'H' => '%H',
        'i' => '%i',
        's' => '%s',
        );
      $format = strtr($format, $replace);
      return "DATE_FORMAT($field, '$format')";
    case 'pgsql':
      $replace = array(
        'Y' => 'YYYY',
        'm' => 'MM',
        'd' => 'DD',
        'H' => 'HH24',
        'i' => 'MI',
        's' => 'SS',
        );
      $format = strtr($format, $replace);
      return "TO_CHAR($field, '$format')";
  }
}?>

The example view I've given is also effected by the format_date() issue in http://drupal.org/node/894560, which is how I tripped over it :)