When G4Material is constructed by G4NistMaterialBuilder::ConstructNewIdealGasMaterial and either pressure or temperature is changed from STP, both pressure and temperature are set to STP. This may be because faulty coding at file G4NistMaterialBuilder.cc, line 401, if(temp != STP_Temperature && pres != STP_Pressure) I think it should be if(temp != STP_Temperature || pres != STP_Pressure)
Dear Shoichiro, thank you very much for this post. You really identify a bug in material constructor. The fix is already integrated into Geant4 development version and will be available with the next public release/patch to Geant4. best regards, Vladimir