We detected and solved an issue saving fit parameters in configurations which contain several interband transitions. When you load such a configuration some fit parameters may point to the wrong susceptibility. If you recompute the optical model the result is a kind of garbage, in most cases.
If you are experiencing this problem you should load the configuration and delete all fit parameters before you update the optical model. It is then safe to generate new fit parameters and save the configuration using program versions generated after June 2, 2015.