Volume level adjustment

I have setup volume level adjustment with sliding rate.

Ex. I have setup Base price = 100 $

      Sliding rate from 100 EA - discount 10% of base price.

                         from 200 EA - discount 20% of base price.

Now entering an order of 200 EA. It is giving $5 discount of base price $100, so unit price is 95$. which is ok as per the calculation. but if i run R42950 after that. Unit price is again recalculating and coming as 100$ in the order.

I understand i can run reapply volume level pricing report , which will reflect the correct price again.

May i know, why it is happening ?

Thanks,

Vishal