Hi,
I know this thread is old, but I experienced the same behaviour and in my case it was an error from my part because when I was declaring the metaboxes I used the same id for all of them as
$meta_boxes[]=array(
'id'=>'general',
'post_types'=>'people'
If I set a different id for each metabox field group it works fine. According to the documentation the field group id should be unique, but I thought that since I only have one metabox field group for each CPT that won't be a problem. But it is.
Hope this helps someone!
