the_post_thumbnail problem

hi

I’m trying to use the_post_thumbnail with my own parameters, but it always comes out with the defaults. i’m building my theme on top of twentyten as a child theme.
this is my code:

add_image_size( 'jp-gallery-list',  500, 180, true );
if (is_category()) {
	global $post;
	$args = array( 'numberposts' => 5, 'offset'=> 0, 'category' => get_query_var('cat') );
	$myposts = get_posts( $args );
	foreach( $myposts as $post ) :
		setup_postdata($post);
		?>
		<a href="<?php the_permalink(); ?>">
		<?php
		if(has_post_thumbnail()) {
			$thumb_attr = array(
				'class'	=> "gallery-list-thumb",
				'alt'	=> the_title_attribute(array('echo' => false) ),
				'title'	=> the_title_attribute(array('echo' => false) ),
			);
			the_post_thumbnail('jp-gallery-list', $thumb_attr );
		}
		?>
		</a>
		<?php
	endforeach;
}

however, the output is

<a href="https://www.luciatallova.com/blur-minds-clear-sights/">
<img src="https://www.luciatallova.com/wp-content/gallery/znova-nemozem-zaspat/thumbs/thumbs_165166_499474188633_99323968633_6311917_732718_n.jpg" alt="165166_499474188633_99323968633_6311917_732718_n" title="znova nemozem zaspat" class="wp-post-image ngg-image-1 " />
</a>

which is wrong – or rather default…

thanks for comments!