  The Optimal Filtering (OF) reconstruction of the sampled signals from a
particle detector such as a liquid ionization calorimeter relies on the
knowledge of the normalized pulse shapes. This knowledge is always imprecise,
since there are residual differences between the true ionization pulse shapes
and the predicted ones, whatever the method used to model or fit the
particle--induced signals. The systematic error introduced by the residuals on
the signal amplitude estimate is analyzed, as well as the effect on the quality
factor provided by the OF reconstruction. An analysis method to evaluate the
residuals from a sample of signals is developed and tested with a simulation
tool. The correction obtained is showed to preserve the original amplitude
normalization, while restoring the expected $\chi^2 $--like behavior of the
quality factor.
