  Drell-Yan pair production is investigated. We reexamine a model where the
quark momentum fraction is defined as the ratio of the corresponding light cone
components of the quark and parent nucleon in a naive parton-model approach. It
is shown that results differ from the standard parton model. This is due to
unphysical solutions for the momentum fractions within the naive approach which
are not present in the standard parton model. In a calculation employing full
quark kinematics, i.e. including primordial quark transverse momentum, these
solutions also appear. A prescription is given to handle these solutions in
order to avoid misleading results. The impact of these solutions in the full
kinematical approach is demonstrated and compared to the modified result.
