I found this article about "post formats" in the Codex:
It says" "Note: When writing or editing a Post, Standard is used to designate that no Post Format is specified. Also if a format is specified that is invalid then standard (no format) will be used."
So I wonder if this has something to do with it. I don't believe my theme (ProSense) supports post formats, since I don't see any options for selecting a format or "post type" when composing a post.
I'm hesitant to start fiddling with the code since this "issue" is, as far as I know, not causing any "problems". But like the OP, I'd like to understand why it's affecting only one post.
Any advice here would be much appreciated! i.e. can I just append:
// add post-formats to post_type 'page'
add_post_type_support( 'page', 'post-formats' );
// add post-formats to post_type 'my_custom_post_type'
add_post_type_support( 'my_custom_post_type', 'post-formats' );
to the end of my functions.php file?
But where do I define my custom post type?