ONLY one custom post type appears on index, defying my query_posts

Hi!

So, I have multiple custom post types that I’d like to have appear on my homepage, including:
post, articles, questions, resources.

Accordingly, my query_posts is written in loop.php as follows:

<?php query_posts( array( 'post_type' => array( 'post', 'articles', 'questions', 'resources' ))); ?>

Yet, only posts of type articles are appearing on index.html.

I’ve walked into a company that runs a zillion odd plugins and the Open theme, so I suspect there’s a config issue that I haven’t tracked down.

Where are some more places I could look to resolve the issue?