ArcGIS 10.2 Model builder Spatial Join user input

Question

I have a model that runs a spatial join and then adds and calculates fields to that joined table output. The model is designed so that a user can change the target features and join features. I have also added the field map as a parameter. However, when changing the target features and join features (when ran as a model tool) no field map is generated, so no information is outputted. Thus, no fields are calculated afterwards, even if the model successfully ran.