This may be meaningless giving all the twists and turns in this episode, but Jack would not have been on the stand before the procecutor was to question Kate's mom. In real life trials the procector/plaintiff present their case first, then the defense presents their case. I suppose the writers/producers did it this way in order to get Jack on the stand. If the procecuter had gone first (as in the real world), no mom, case over--no Jack on the stand.