ModifySlabs through ACAPI_Element_Change applies only the fill type; origin and distortion matrix get reset to (0,0) and identity, version goes back to 0, and the call still returns NoError. The author tried six masking variants on Archicad 29 and every one reset, and no other DevKit API writes it; the fix is to report the ignored value back to the caller instead of pretending it stuck. Any agent driving Archicad through this would believe its edit landed.