Private Group pop-out email

We have a couple of Private Groups set up, one for IT and one for HR. Everything is working as far as the groups go, but what I was wondering is why we can not Double-click on an email to have it pop-out to full screen? This works on every other mailbox, and Public Group, but not Private. I assume this is a built-in restriction, but I don't know why.

Has anyone run into this, and is there a solution at all?

Thanks!