orderby not working

I’m trying to display some posts and order them by modified date. I’m printing out the query and no matter what I change the orderby to, it never has it in the query. Here is what I’m using:

[display-posts orderby="modified" order="desc" taxonomy="category" tax_term="whats-hot" image_size="directory-image" posts_per_page="6"]

and here is the query it’s generating:
SELECT wp_posts.* FROM wp_posts WHERE 1=1 AND wp_posts.ID = 22 AND wp_posts.post_type = 'page' ORDER BY wp_posts.menu_order ASC, wp_posts.menu_order ASC

What am I missing?

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