Media cpt-onomies not registering

Hello,

I have several CPTs, attached as CPT-onomies to Media. However, within the media attachment edit screen, when I attempt to select one of these CPT-onomies, it does not register. When I hit ‘update’, the selection disappears. I have tried this with WordPress 4.4 and 4.5 and 4.6, and have tested all possible plugin conflicts. This would be an awesome part of this plugin were it to work properly! Any help would be gratefully appreciated.