Node Relationships (noderelationships) uses #after_build to add some CSS classes, on which the javascript that renders the buttons depends.
When content_profile_registration adds the profile node form to the user registration page, it only adds certain elements, notably skipping over some #-prefixed attributes including #after_build.

I'm not exactly sure how to categorize this or which project to file it under.
I'm guessing maintainers for both projects will have arguments as to why it's a bug with the other's module.

I filed a related issue in NR queue, but haven't heard anything.
#1243016: Incompatible with Content Profile User Registration

Has anyone else figured out a workaround for this?