A big trouble with fusion

Hi,

the following code in Visual C++ fuses a cylinder with a ball and tries to visualize the result in OCC v.4.0. However the sample bails out with an unhanded exception somewhere in the poly_triangulation module. It works fine if Xc is 1e-3 and the visible result is also correct. If Xc is 0 then the visualized solid disintegrates into a disk and a half of a sphere - the result of the fusion which is (supposed to be) a solid is turned in two faces!

The questions are:

1. Is it a problem with visualization (triangulation?) or the underlying topological structure is broken?
2. What is the workaround?

With the hope to get help,
Aleksey

P.S. I am not very much familiar with OpenCascade yet but have to decide either it is a suitable library for our project related to 3D modeling. It is confusing that such a simple example is so troublesome and the first idea is that I am doing something wrong but checking the OCC docs does not reveal that I use the OCC objects in any non-natural way.

void CTestViewerView::OnTest() {
Standard_Real r = 10;
Standard_Real h = 50;
Standard_Real Xc = 1e-6;
Handle(AIS_InteractiveContext)aContext;
aContext = this->GetDocument()->GetAISContext();
BRepPrimAPI_MakeCylinder cyl (r,h);
BRepPrimAPI_MakeSphere sphere (gp_Pnt(Xc,0,0),r);
BRepAlgoAPI_Fuse fused (cyl.Solid(),sphere.Solid());
aContext->Display(new AIS_Shape(fused.Shape()),1); // crashes
}