Hi @elliot
I would expect any custom fields generated by ACF to be hidden from WordPress’ custom fields drop-down list. Especially if these fields are not associated with the post type being edited (i.e. ACF fields assigned to a custom post type should not be visible when editing a page post type).
How this is achieved is not important to me, although using the underscore prefix in the ACF plugin’s code is probably the simplest method.
