I have a hierarchical custom taxonomy defined on the attachment post type. The Media > Library option correctly displays the taxonomy terms in a hierarchical category-like metabox.
When I open an image for editing in the new Insert Media overlay, the hierarchical custom taxonomy is displayed with a tag-like single entry field and no list of the pre-defined taxonomy terms, instead of with the desired category-like list of terms with checkboxes.
Is this intentional or a bug? Is there a workaround?