I've run into an interesting error when using a posts-populated select field. Once I create a new post in a custom post type, I get the following PHP warning:
First parameter must either be an object or the name of an existing class in /Applications/MAMP/htdocs/.../developers-custom-fields/slt-cf-init.php on line 409
I haven't thoroughly tested yet, but I think the issue is that as the post has not yet been saved we don't currently have a global $post set and so this function throws an error. It seems to be a fairly harmless error as the options_query is still displaying posts properly and I could easily suppress the it, but I thought it'd be worth while looking into, rather than attempting to cover-up the issue!