PRE and CLR

Hi i am simulating a D Flip Flop with CLR and PRE

Both PRE and CLR are active low.

Why is it that when i put PRE and CLR low simultaneously, both my Q and /Q will be a 1. Is there an explanation why this happens?

I am writing a report on the simulations i did but i can't seem to find a book that explains why this happens.

Hello,

may be on the datasheet of the flip flop there is the internal scheme and then you can understand the way they design it...