Token Suport in Self Service Flow Steps

Hi, 

I have been trying to implement a flow step service using the documentation outlined here

The documentation clearly states you can use my.tokens in the flowstep context. I have tried many times to do this and have found the tokens to not populate and instead the raw string token key is passed. Below is the payload that is received by my service from Marketo in a 201 POST request.

Given that this is a relatively new feature to Marketo I am potentially thinking this may be a bug? 

Here is my declaration in the getServiceDefinition.

When I create the service in Marketo I can see that I am giving permission to use my token context. 

Please may someone from the team assist me in understanding how this is to be properly used?

Many thanks,

James Baird