raffav

my solution is 2 loop, the first

$agenda = get_posts('category=4&numberposts=10');
	<?php
// an empty array
$date_order = '';
if( $agenda ) : ?> <?php  foreach( $agenda as $post ) : setup_postdata( $post ); ?> 

<?php 	$custom_date = get_post_custom_values('custom_date');
	if (isset($custom_date[0])) {
	$evento = strtotime($custom_date[0]);
	} else {
   $evento = strtotime($post->post_date_gmt);
			}
	$date_order[$evento] = $post->ID;

// now the array contain key as date and post ID as value
	 ?>

	<?php endforeach;  ?>
 	<?php endif; ?>

// and the second

// order the date in the custom field
ksort($date_order);

foreach ($date_order as $key => $val) {
 query_posts('p='.$val);
global $more;
$more = 0; 

// the second Loop
while (have_posts()) : the_post(); ?>
// your stuff here
	<?php endwhile; ?>
 <?php	} ?>

in this way i can order post with or without date custom field
there are too many query?
it’s too many expensive?

this code work for me

get_categories( 'orderby=rand()&hide_empty=1&include_last_update_time=1&hierarchical=1&number=6&exclude=5,25);

i simply tried to overwrite the orderby functions with a different possible options [rand()];
i hope this help to solve the bug.