I just noticed that when editing a set of subscribe buttons, at the top of the page and in the browser tab it says “Edit post”. I believe you may have set up your custom post type incorrectly or just left out part of the definition. You should give it a name to use as singular. I think that would solve the problem.

From what I can tell, you need this line in the labels array:

'edit_item' => __( 'Edit Subscribe Buttons' ),

Hate to nit pick, but I’m trying to trouble shoot something and with so many tabs open it would be nice if your tab was labeled correctly.

Thanks for the plugin.