ICC should adopt a new policy of not allowing the umpires whose countries have reached the semi final to umpire in the other semi final. So if four countries have reached the semi finals, then none of the umpires from these 4 countries be allowed to umpire in the semi finals.
Umpires are also human and sometimes favortism and preferences might creep in when making a decision.
This might have also been the case in the Pakistan's semi final against NewZealand. No doubt Simon Taufel is an excellend umpire, but at times umpires may make a decision to favor their own team ?