Why is RobotState not the same in different nodes?

edit

I am attaching a collision object to my robot. The object is displayed fine and reported correctly as the cause of a collision if I move it into a wall in Rviz. I also added some debug messages that make it clear that the RobotState in the move_group node knows about this object.

However, I have two other nodes running, which have a move_group_interface and a MoveGroupCommander in C++/Python respectively, and neither of their RobotStates seem to be aware of the attached object. They are both running when the AttachedCollisionObject is published, but their state does not change.

I check with this code in the C++ node:

robot_state::RobotState state(*group_interface.getCurrentState());
std::vector<const robot_state::AttachedBody*> ab;
state.getAttachedBodies(ab);
ROS_INFO_STREAM("Current state has " << ab.size() << " attached bodies.");

But the result stays 0, even though it should say 1 after attaching the object (a similar debug message does report the correct number in the move_group node).

Normally it would not be a problem since the collisions are checked in the move_group node, but I need these attached objects to construct my planning goal. What am I missing? How can I update the RobotState? Thanks in advance.

I build MoveIt from source on the kinetic-devel branch and use ROS Kinetic on Ubuntu 16.04.

edit: I am using the PlanningSceneInterface to attach the collision object and not publishing a message manually, if that makes a difference.

edit2: I may have found the reason for this behavior in the description of the PlanningSceneInterface applyAttachedCollisionObject function:

Other PlanningSceneMonitors will NOT receive the update unless they subscribe to move_group's monitored scene

I'm not sure how to do that or why that wouldn't be the default behavior of the move_group_interface, but any pointers are welcome.