When viewing course blogs on a course with group mode set to separate as member of a group there are a couple of things wrong:

1. Double up of the "blog entries" in the navbar.
2. Failing to set the course if the user is not a member of any group.

This was picked up while testing MDL-36215, I tracked it down to blog_get_headers at which point I decided this should be a separate issue (as that is a really awful function).