Key points are not available for this paper at this time.
Reinhard Bergmann, John Ludbrook, Will P. J. M. Spooren, Different Outcomes of the Wilcoxon-Mann-Whitney Test from Different Statistics Packages, The American Statistician, Vol. 54, No. 1 (Feb., 2000), pp. 72-77
Bergmann et al. (Tue,) studied this question.