we cannot gauge Divine logic..

The theory of Karma forming a vital part of Hinduism is not easily comprehensible anyway..

One explanation, perhaps the most plausible one, is that what the human mind conceives life as occurring in separate compartments.. Like this life, earlier life, and the life that would come-- are all viewed by the Controller as a continuum. And since He sees the entire string of births, from beginning to end and would outlive all such episodes, there is nothing illogical in His action of meting out punishment in one life for the misdeeds of another life. And the question of immediate punishment-- our life is very short- at the most hundred years-therefore an hour or a day look substantial to us.. But in Gods clock, a day, a year a millennium, and even bigger time-slices would appear to be too tiny .in comparison to the infinite time that He governs.. So it is too difficult to test God's logic with the evaluation and tools of validation provided to our mind whose endowments are far too limited. 

यतो वाचो निवर्तन्ते अप्राप्य मनसा सह Taittireeya Samhita.. Krishna Yajurveda

If one is curious about or even if he is baffled about Gods logic, it is okay..

But usually if one challenges Gods logic, it will not be okay for him because he is breaking his head against a huge mountain. Anyway everything is Okay by God.

We believe by sheer trust or faith many things which are apparently illogical. Even small things in our day to day life conform to that category.

So in respect of such great issues, we cannot do anything, just for want of adequate data and panoramic vision too (to cover the huge time-span)