When adding the post_formats_compat the_content filter a post ID argument should be included
|Reported by:||gcorne||Owned by:|
The new post_formats_compat() function relies on knowing the $post_id to get meta data for the post format. By default, the function is bound as a the_content filter, which doesn't pass a $post_ID. One possible solution is to change the number of accepted arguments when adding the filter to 2, although this will require third-party developers that are calling apply_filters( 'the_content', $content ) with an unset $GLOBALS['post'] or the global set to a different post to pass in the post id: apply_filters( 'the_content', $content, $post_id ).
wp-includes/comment.php:1752 is an example from core of using the_content on content that is not pulled from the global $post.
For completeness, it may make sense to do the same with the prepend_attachment filter.