I find that when placing more than one G4PVParameterised volume in a mother volume, G4 seems to get confused with volume numbers; it ignores the subvolumes in the parametrised volume and reports copy numbers as -1. It also begins to report "G4Tubs::DistanceToOut(p), point p is outside !?" exceptions that are not reported when only a single parametrised volume is used. More generally, it occurs when I add a G4PVParameterised volume to any mother volume that contains any other daughter volumes. I have created this latter case as an example program that recreates which I can email to any interested parties.
By definition one mother volume can have ONLY ONE parameterized volume. Also, once it has a parameterized volume, it must not have any other daughter volumes by ordinary placement.