Private category: no preview of the topic on link

I notice on my forum if a share a link of a public topic on a private or public topic there is a preview like this :

But if I share a private topic on the same private topic or another one also private, there is no preview, just a link (a made an error on this link to show you the result)

By private i mean not all the community can read the post, only a group !

Version : v1.7.0.beta5 +45

This is not a bug; the requests to onebox are public requests. You can browse #releases to see what our plans are here.