This was brought up on the issue tracker too: https://github.com/ros2/ros2/issues/303
I think the consensus was that this broke in some recent refactoring of the type support and that we’re not going to spend time on fixing issues with opensplice at the moment (see ROS 2 alpha8).
If this matters to you, then you can chime in there or work on a fix with guidance from us where necessary.