In geant4.9.5.p01 I happen to be looking at G4SIunits and see that the "degree" definition is inverted from what is correct: static const double degree = (3.14159265358979323846/180.0)*radian; It looks like G4SIunits.hh are not used in the rest of the G4 source so this is only a potential problem but may bite someone someday if not fixed. -Brett.
The definition of 'degree' in G4SIUnits (and in CLHEP) is correct, as it relies upon transformation from radians, where 'radian' is considered as unit.