BrepFaces have a reverse orientation flag, which allows you to flip the normal without affecting the underlying surface. This is an important optimisation because half the time a brep-face needs to be flipped when it is joined with other faces, so this flipping needs to be as minimal an intervention as possible.
Surfaces do not have this. The normal direction of a surface is determine by the right-hand-rule and the UV directions. When you convert a BrepFace into a Surface, you lose the OrientationIsReversed information.