In my Tridion Reference Implementation website, I have defined a model with a set of properties, which map to fields of my published components. The TRI code is able to map these fields nicely to my model class, so in my component, i have a name and description. In my model class, these two properties nicely take the value of those fields in my component. This is something that the TRI does out of the box, using a class named DD4TModelBuilder.
Now, I added a couple of extra fields to my component's schema, added some values, and published these components.
I also added extra properties to my model class. Unfortunately, these fields stay null, so somehow, the Model Builder seems to ignore my new fields (old fields still work as before).