during Linux compilation we always get the following message /afs/cern.ch/sw/geant4/releases/share/geant4.3.0/include/G4MagneticField.hh:48 warming: base class 'class G4Field' should be explicitely initialized in the copy constructor.
Minor fix introduced in development tag "field-V03-00-00". Will be available in future patches or bug-fix releases. Thanks.