If you createany construction surfaces, within the Superfeature,with offset curves that happened to use pre-existing curves as the parents, that surface cannot be layered off later as the Superfeature keeps holdof it and thinks it's part of the merged subfeatures. The result is, you will not be able to solidify or thicken.
I forgot about that little gem today and had to undo about two hours worth of work. Save often.
Your welcome to use my student resources: http://vleblog.lboro.ac.uk/cad/sample-page/3d-modelling/surface-modelling/isdx-freeform-surface-modelling/