Why does this game think , that my vassal's general is good enough to lead the fight ?

I have a problem with this shit , and this problem causes me to lose every battle. The game thinks that my vassal's general is better than my 4 shock one , and I dont agree with that !!! But not only that , when his general gets to lead the fight IT SIMPLY DOESN'T ROLL ANYTHING !!! So apart from the Random Dice , nothing ..... why is that ? is that a bug ?It should roll a 1 or something , not nothing , seriously ?