It is important for an optical pattern recognition filter to produce a localized correlation response without significant sidelobe structure. This paper notes, and investigates further, the high degree of robustness of the correlation response of a wideband filter in the face of severe frequency domain modulus disruption. The phenomenon is demonstrated by simulation, and analysis is presented to explain the observations. This property may be of value in filter design by allowing the relaxation of frequency domain constraints in the knowledge that correlation peak structure will not drastically deteriorate.