If a user proxies an image on b.net, it renders on all of these domains. However, if they copy b.net's image and post it in another post (or in our chatroom) on a.com, it breaks. The same goes for Link Proxies. All of this applies to HTTPS/HTTP, too, which means the issue can be replicated on native XenForo without the XenCentral multi-site domain add-on.
It causes a big problem where if, you're on https://b.net and someone links you to b.net, it will give you a cross-site warning via the link proxy.
Is there any way to tell the proxy that all of these domains are the same server?