doc: the shell tutorial should specify that #returns needs to be called

[doudou]

I'm having a problem related to the Roby- tutorial, and was wondering if anyone here could help me understand what is going wrong.
I'm currently following the part of the tutorial called "Interactive Shell", which can be found here: http://rock-robotics.org/stable/api/tools/roby/tutorial/shell.html

As instructed in the tutorial, I start the Roby application, by running:
$ roby run -rgoForward -c

The application starts as expected. Then, I ask the robot to move forward, by running in a separate Roby shell:
localhost:48902 > move! :speed => 1

However, this causes both running processes to emit an error. The error message is:

(Roby) invalid replacement: missing provided models Main::Move

Main::Move was defined as described earlier in the tutorial - so I don't understand why it seems to be missing. Any help resolving this issue is appreciated!