When opening a saved project that contained a surface model, the surface model is not displayed in the data manager.
The surface model was created by right-clicking on the segmentation and selecting "create smoothed polygon model".
However, zipinfo applied to the saved *.mitk project shows that the surface model in form of *.vtp object is present.
This was tested using the /E130-Daten/3M3 Demodaten/GeneralTestingData/CT_heartLarge_3DT.pc.gz