Space duality and quantized Wilson lines

We discuss space duality of the bosonic and heterotic string compactified on toroidal orbifolds, allowing for the most general modular invariant background. This includes discrete axionic background fields as well as quantized Wilson lines. The latter are known to reduce the gauge symmetry and to lead to (0,2)-models. We show that the canonical generalization of torus duality is not a transformation in moduli space. Instead it turns out to provide a map from a symmetric to an asymmetric orbifold. For duality to be a symmetry in moduli space one has to define a different transformation. (orig.)