Bug? Edit → Remove - SelMVerts

Hi there, my aim is to calculate the inner volume of prehistoric cups an jars. I have 3d models of restored vessels, which are preserved by 50 to 80%. My idea was to extrude profile polylines, then cut by plane ("Eichstrich", ca. 2 cm under rim), then calculating the volume. Extruding was sucessfull, but why this difficult way described in the tutorial (https://gigamesh.eu/tutorial/extrude_profile_lines/)? You can extrude any other profile polyline produced this way: https://gigamesh.eu/tutorial/profile_lines_and_cross_sections/ But anyway, using both methods, Gigamesh crashed on the last step, removing the original 3d-data: Edit → Remove - SelMVerts.