  In realistic four-dimensional string constructions the presence of anomalous
U(1)'s is generic. In addition, the associated Fayet-Iliopoulos contribution to
the D-term can break the extra gauge symmetries. As a consequence, physical
particles can appear combined with other states. We show that even if a
three-generation standard-like model has originally flavour-independent soft
scalar masses, the particle mixing contribution may generate non-universality
among them. Thus FCNC effects which were apparently absent reappear. We also
discuss the size of these contributions in an explicit model, and how they can
be suppressed.
