[Z288racer]

I have changed front Rotor pads once and everything seemed normal. I just changed them for the second time (and first time for the rear) and I noted an unusual indentation into the front rotors. It looks like the pads put in a bead into the rotor. (See pictures). This happened on both sides of the rotor and on both front rotors. The result is that the cross section of the rotor where these indentations are is below the minimum thickness of the rotor. Anyone seen anything like this? What is the cause? Is this safe to race??? PS I only wore down the pads to around 5mm.