This is just one of a number of issues with this listener type. We're currently debating the best approach to take on these, so stay tuned. One way or another, those composers will be changed to implement the MessageComposer interface, it's just a case of when. We're not sure of the logic as to why it wasn't done this way to start.
Just to put Tom's comments into context, remember that we inherited a lot of the core code through a partner donation.