frame id is overridden when collision object added to planning scene

I am following the ["Adding Collision Objects to the Planning Scene"](https://ros-planning.github.io/moveit_tutorials/doc/move_group_python_interface/move_group_python_interface_tutorial.html#adding-objects-to-the-planning-scene) section of the MoveIt! Move Group Python Interface guide. I have been setting the `frame_id` of the `PoseStamped` messages to `"/map"`. However, when the collision object is added to the planning scene, I find that the `frame_id` has been changed to `"/odom"`. I have also noticed the following log message, "Listening to '/collision_object' using message notifier with target frame '/odom'". This message seems can be found in [line 1055 of planning_scene_interface.cpp](http://docs.ros.org/kinetic/api/moveit_ros_planning/html/planning__scene__monitor_8cpp_source.html#l01055) as a result of `tf_ == true`. Why is this happening?