The transverse mass calculation used was updated to reflect common practice at hadron colliders. In the previous iteration, the mass calculation used is not common at hadron colliders, as it does not give a peak at the parent particle mass. The updated version reflects the recommendation of PDG 49.6, and is relevant for decays such as W->e,nu (or H->yyd) where part of the decay is invisible. The common expression is:
sqrt(2pt1pt2*(1-cos(dphi)).
This update is now reflected in the hypo calculation.