When creating a Curtain System, they should be created separately on each orientation and for each wall of the project. If Curtain Systems are placed on several orientations and on several different areas of the model at once, it will be read as one object and separating these out into Facades and Surfaces will not be possible.
Creating multiple curtain systems at once in Revit, provides information to the application for one system with a number of grids. The application will get an average orientation across all grids. This could lead to unexpected orientations and results. It is best therefore, if ‘Select Multiple‘ is not used during Curtain System creation.
Curtain System creation is most compatible when the glazed walls are modeled in separate editing sessions in Revit.