G4VSteppingVerbose is a singleton class that holds its instance in G4VSteppingVerbose::fInstance static field. This field is initialized in G4VSteppingVerbose::SetManager method but does not seem to be cleared anywhere.

Suggested fix:

File: G4VSteppingVerbose.cc
Method: G4VSteppingVerbose::~G4VSteppingVerbose

G4VSteppingVerbose::~G4VSteppingVerbose(){
  fInstance = 0; // <-- this is the patch
}