Extruded solid: Bug in the triangulation

The following code:

int nVertices = 8;
int nSections = 4;
vecgeom::XtruVertex2* vertices = new vecgeom::XtruVertex2[nVertices];
vecgeom::XtruSection* sections = new vecgeom::XtruSection[nSections];

vertices[0].x = -30; vertices[0].y = -30;
vertices[1].x = -30; vertices[1].y =  30;
vertices[2].x =  30; vertices[2].y =  30;
vertices[3].x =  30; vertices[3].y = -30;

vertices[4].x =  15; vertices[4].y = -30;
vertices[5].x =  15; vertices[5].y =  15;
vertices[6].x = -15; vertices[6].y = -15;
vertices[7].x = -15; vertices[7].y = -30;

sections[0].fOrigin.Set(0, 30,-60); sections[0].fScale = 0.8;  sections[1].fOrigin.Set(0,-30,-15); sections[1].fScale = 1.0;  sections[2].fOrigin.Set(0,  0, 10); sections[2].fScale = 0.6;  sections[3].fOrigin.Set(0, 30, 60); sections[3].fScale = 1.2;

vecgeom::SimpleExtruded solid("testExtruded", nVertices, vertices, nSections, sections);

has failed with the following message:

Assertion failed: (counter < nvertices && "Triangulation failed"),
function CreateTessellated,
file /Users/evc/VecGeom/volumes/ExtrudedStruct.h, line 200.
Abort