post_thumbnails breaks themes

You have a function called "post_thumbnails" that modifies $_wp_theme_features directly (obviously you're not supposed to do that, the leading _ denotes that as a private variable). The problem is that if a theme as post-thumbnails activated for all post types (set to true) you mess that up. After your function runs, it only supports for post, page, and product.

You can fix it by doing NOTHING if $_wp_theme_features['post-thumbnails'] is already true.