This is something really nice. And Actually, just a suggestion, this would be really useful if integrated with your Social Forums addon so social forum owners can even setup a page for non-members of group, members, etc..
This is as designed for now. If members couldn't see code they had written for user groups they were not a part of, it would add all sorts of complications (i.e., users posting for guests and then not being able to edit it), so you'd have to block members from posting to user groups they were not a part of completely (or make it permission based). Happy to discuss though.