I created a custom post type called "Images" and a custom taxonomy "Galleries" to group these image entries together.
I do not want "Galleries" to be hierarchical but I just need tags therefore 'hierarchical' => false
If I add the galleries via the main page they are saved and shown properly.
The problem is when I add a new post "Image" and I want to pick up an existing gallery in my meta box, no tags are shown and I get the "no tags" message.
If I add my galleries (tags) using the meta box they are actually saved and shown correctly. It is only adding the tags through the main page which does not work. It works if I set 'hierarchical' => true but I do not need categories, I just need tags.