the_title() does not show but the_execerpt()

Hello,
on a page (not homepage) I have this code:

$args = array( 'posts_per_page' => 3 );
$lastposts = get_posts( $args );
foreach ( $lastposts as $poster ) :
echo get_the_ID();
setup_postdata( $poster ); ?>
	<h2><a href="<?php the_permalink(); ?>"><?php the_title(); ?></a></h2>
	<?php the_date(); the_excerpt(); ?>
<?php endforeach;
wp_reset_postdata();

the_execerpt() shows correctly 3 different values (from the posts), but all other functions show the values from the page where I placed the code.
The page ID is in my case 678, so the_ID() shows 3 times 678,
the_permalink() links to the page 678 and the_title() shows 3 times the title of the page.

Any idea ?
Best regards, Uwe