Thanks for providing with the code, maybe Mefistotelis can make some sense out of it. 
I cheaked the experience levels (named as LevelsTrainValues, right?) of the party in question, but they all seem pretty much the same, and would more support the fact of 'the strongest leads'.
Code:
CREATE_PARTY(ELITE)
ADD_TO_PARTY(ELITE,SAMURAI,9,1000,ATTACK_ENEMIES,0) <- 16000
ADD_TO_PARTY(ELITE,WIZARD,8,1500,STEAL_SPELLS,0) <- 13000
ADD_TO_PARTY(ELITE,BARBARIAN,8,1000,STEAL_GOLD,0) <- 13000
ADD_TO_PARTY(ELITE,GIANT,7,1000,STEAL_SPELLS,0) <- 10500