get_the_excerpt() removes all p tags in page!

Question

I have written some shortcode to be able to place the latest post excerpt anywhere on the page, but I got a problem that I have trying to solve for days now! And I can't find the reason why the get_the_excerpt() removes all p tags around text in other parts of the page. When I remove get_the_excerpt() from the code, it's no problem with the other text inside other shortcodes, but when I put i back, the problem is back! Please have a look at the code and tell me what I have done wrong or could improve! Thanks!

function show_posts() { global $post;
$html = "";
$extra_css = "";
$latestPosts = new WP_Query('cat=5&posts_per_page=1');
if($latestPosts->have_posts()): while($latestPosts->have_posts()): $latestPosts->the_post();

if (has_post_thumbnail()) {     
$extra_css = "has-thumbnail";}
$html = "<div class='wide'><article class='post {$extra_css}'>";
$html .= "<div class='post-thumbnail'>";
$html .= "<a href='" . get_the_permalink() . "'>" .     get_the_post_thumbnail(null,'thumbnail') . "</a>";  
$html .= "<div class='post-thumbnail-date'><h4>" . get_the_time('Y-m-d') . "</h4>   </div>";
$html .= "</div><!-- end post-thumbnail -->";
$html .= "<h3><a href='" . get_the_permalink() . "'>" . get_the_title() . "</a></h3>";
$html .= "<p class='post-info'>" . get_the_time('Y-m-d') . " | Av " . get_the_author() . "</p>";
$html .= "<p class='post-text'>" . get_the_excerpt() . "</p><p><a href='" . get_the_permalink() . "'> Läs mer...</a></p>"; 
$html .= "</article></div>";
endwhile;
else:
// Error message
endif;
wp_reset_postdata();
return $html;
}
add_shortcode('blogg','show_posts');