Category Exclude from Single Post doesn't seem to be working

I’m using this in the navigation for single pages:

<?php if(get_adjacent_post(false, '7', true)) { ?>
        <img src="<?php bloginfo('template_directory'); ?>/images/g_leftarrow.png" />
        <li><?php previous_post_link('%link') ?></li>
<?php } else {
      /*nothing*/
} ; ?>
|
<?php if(get_adjacent_post(false, '7', false)) { ?>
	<li><?php next_post_link('%link') ?></li>
	<img src="<?php bloginfo('template_directory'); ?>/images/g_rightarrow.png" />
<?php } else {
	/*nothing*/
} ; ?>

It was working a week or so ago, but the posts in category 7 are now being shown in the navigation. I’ve checked for any changes; the posts to be hidden are still listed under the correct category, and that category (exclude) does indeed have the ID of 7. I don’t know what else could be interfering with the navigation. Any ideas would be greatly appreciated.

Thanks.