Repeating Results w/ Category Filtering

I’m using this to display featured images in a js “image slider”. Since either 3.1 or (more likely) my own user-error, it results in only the 2nd-oldest post’s featured image displayed for each of 5 instance of $slide. Meanwhile, the_content() displays all 5 posts’ text just fine.

See it in action

//Displays featured images of posts with 'masthead_slider' category

			$slider_args = array(
				'category_name' => 'masthead_sliders',
				'numberposts' => -1,
				);
			$slider = get_posts($slider_args);
			foreach ($slider as $slide) : setup_postdata($slide); ?>
				<div><?php the_post_thumbnail($post->ID); the_content();?>
				</div>
			<?php endforeach; ?>

Thanks for any help on this!