Motion compensated de-interlacing and motion estimation based on Yen's generalisation of the sampling theorem (GST) have been proposed by Delogne and Vandendorpe. Motion estimation methods using three-fields have been designed on a block-by-block basis, minimising the difference between two GST predictions. We will show that this criterion degenerates into a two-fields criterion, leading to erroneous motion vectors, when the vertical displacement per field period is an even number of pixels. We provide a solution for this problem, by adding a term to the matching criterion.