Let's see if this site will let me post anything today....Okay, the step in the profile is 20mm, the rise is 10mm. There are internal fillet and an external, meeting on their quadrant points, 10mm radius. The edge of each fillet refers to the plane of the 20mm step...which no longer exists. If you want to suppress the fillets at some later point, perhaps to resize them, the kernel has to either keep a reference to that plane in the history, or have the smarts to figure out where it should go, and files, depending on how the objects have been built, don't always retain that. The theory of resilient modelling is to make the step 20.0000001 deep so that there's always a vestige of the feature, a narrow strip of the face, remaining to refer to. It's below the resolution of your production equipment to physically realise, but it's in the metadata for the program to find.