Hi,

I had a problem with the ILC simulation software Mokka, and I managed to reproduce it with novice example N04: My DetectorConstruction builds 2 nested G4Boxes that have borders in common, as follows:

=============================================================
  G4VSolid * calorimeter
    = new G4Box("calorimeter",100.0*mm,100.0*mm,100.0*mm);
  G4LogicalVolume * calorimeter_log
    = new G4LogicalVolume(calorimeter,Scinti,"calo_L",0,0,0);

...

  G4VSolid * caloLayer
    = new G4Box("caloLayer",50.0*mm,50.0*mm,50.0*mm);
  G4LogicalVolume * caloLayer_log
    = new G4LogicalVolume(caloLayer,Lead,"caloR_L",0,0,0);
  G4ThreeVector layerPos(50.0*mm,-50.0*mm,-50.0*mm);
  new G4PVPlacement(0,layerPos,caloLayer_log,"caloL_P",
                        calorimeter_log,false,0);
=============================================================

With this geometry, when I run /geometry/test/grid_test true

I get a message saying that

GeomTest Error: Overshooting daughter volume
    The volume caloL_P[0] appears to extend outside the mother volume caloM_P[0]
    at the following points in global coordinates: (list truncated)
       length (cm)    ---------- start position (cm) -----------   ----------- end position (cm) ------------
                10                 0           -10           -10                0             0           -10
                10                 2           -10           -10                2             0           -10
                10 
...

This happens while compiling with geant4.9.0.p01 but not with geant4.8.3.

While looking at the above code, we can see that caloL_P is not outside its mother volume.

I also submitted this problem to the Geant4 HyperNews and Tatiana Nikitina
confirmed that this is present in G4 8.3.p01 and later versions

Thank you for your help! 

Gabriel Musat