I just recently bought a dv8 nightmare and i noticed that its seems as if the core/weight block is off. I noticed this because my ball came out of the machine literally. It came out of the machine and when down about 10 lanes and they found it in the back. Someone who has been bowling for 20+ years told me to shake the ball, so i tried just that and i could somewhat feel the core/weight block shaking i was wondering if the cover can separate from the core without the cover being cracked? 

My buddy had a c300 messenger Ti that had the same problem, he threw it so well none of us could tell if it affected anything..as crazy as it sounds!

Could have been a bowling pin the ball return track. Have the shop check it out, usually can determine if the core is separated a few different ways. Most common way is if you blow in the thumb and you feel air come out of the fingers.