Looping through a custom query makes WordPress assume another template [duplicate]

Question

I am calling this code from my custom sidebar, in order to get related postings from the same category:

query_posts(array(
   'cat' => get_category_id(),
   'showposts' => 5,
   'post__not_in' => array(get_the_ID())
));

get_template_part('article-list'); // outputs the posts

This works. The have_posts()-loop inside of my article-list.php now only outputs 5 other postings from the category.

But this also causes a problem: No matter on what kind of page I am (single.php, index.php, ...), WordPress always assumes that I am in the category template. So is_category() always returns true after calling query_posts('cat=...'). Thus is_single() returns false, although the single.php-template is used.

What can I do to tell WordPress that it is still using the single-template? Or: What other function can I use to detect which (main) view is loaded?