get_categories() not showing up in ID order

I am having trouble with some specialty code I had written by a programmer a couple of years ago. Since upgrading to WordPress 2.8, this code is not working properly.

Each category in my blog is a book chapter. Each post is a page of the book. The sidebar is supposed to list the categories in ID order, and under each category, the posts in forward chron order. There is some cookie-related code that precedes the code I’m showing here, to keep it so that your table of contents only goes up through the next post. (Users read in forward-chron, not reverse-chron, order, on this particular blog/book.)

This was working fine through 2.7, I think. But now, the list of categories is in alphabetical order, not ID order, and I can’t figure out why. I have double-checked to make sure that in various upgrades etc. that the IDs of the categories haven’t changed — if the list was in ID order, it would be correct, but it’s in name order, which is wrong. (you can see the sidebar at work here: thenovelette.com/kitty-part-2/055 ).

I’m afraid that I don’t have enough PHP smarts to figure out why this isn’t working or even come up with the simplest troubleshooting. I’d be most appreciative if you could take a look and lend a hand or point me in the right direction.

Thanks so much.

<?php foreach ( get_categories('orderby=ID') as $category ) : ?>
		<h3><?php echo wp_specialchars($category->cat_name); ?></h3>
			<?php $posts = get_posts("category={$category->cat_ID}&orderby=post_name&order=ASC&numberposts=20");
			foreach ($posts as $post) : setup_postdata($post); ?>
			<div class="post">
					<p id="post-<?php the_ID(); ?>" style="padding-top:0px;padding-bottom:0px;margin-top:0px;margin-bottom:0px;"><a href="<?php the_permalink(); ?>" rel="bookmark" title="<?php the_title(); ?>">
					<?php foreach ((array) get_post_custom_values('Episode') as $nvepisode) { $printepisode = $nvepisode; } ?><?php echo "$nvepisode : "; ?>
					<?php the_title(); ?>
					</a></p>
			</div>
		<?php endforeach; endforeach; ?></ul>
</div>