  Non-standard physics which can be described by effective four fermion
interactions may be an additional source of CP violation in the neutrino
propagation. We discuss the detectability of such a CP violation at a neutrino
factory. We assume the current baseline setup of the international design study
of a neutrino factory (IDS-NF) for the simulation. We find that the CP
violation from certain non-standard interactions is, in principle, detectable
significantly below their current bounds -- even if there is no CP violation in
the standard oscillation framework. Therefore, a new physics effect might be
mis-interpreted as the canonical Dirac CP violation, and a possibly even more
exciting effect might be missed.
