Why does `rosnode info <node>` display [unknown type]?

edit

For example -

root@hekateros# rosnode info /hekateros_control
[...removed for brevity...]
Subscriptions:
  * /hekateros_control/follow_joint_traj_as/goal [unknown type]
[...removed for brevity...]

This message type _should_ be trajectory_msgs/JointTrajectory...

Note that this does not affect the execution of the code (i.e. I can still publish messages of the correct type to this topic, and it works correctly)

I would just like to know why rosnode info is unable to display the correct message type information. Do I need to specify a dependency somewhere? And if so, why does the missing dependency not affect message generation, compilation, or execution?

Thanks!

/daniel