To Huntmup and the rest.
You are no longer the ONLY person who had this problem.
I too had almost the exact same thing happen.
My deer (8 pointer) was quartering away at 31 yards (I guessed 30...not too bad...seeing I was up about 20 feet, my pin was right on). I shot, and watched the arrow hit the deer. My first reaction was elation! It looked to be aperfect shot...but an instant later, I could still see more than 3/4 of the arrow!!! We trailed that deer for 2 days!!! Lots of blood, but he kept going. At first, I though: maybe he turned just as the arrow hit him...dumb luck. Now I'm not so sure.
As for expandibles, I shot my deer last year, it WAS broadside, but on the shot it jumped, and tuned quartering TO! The deer was at a rather sharp angle...more than a perfect quarter. The arrow went in just behind the front shoulder (Hit a touch high) and exited the deer at the very back edge of the far lung. 6 seconds, and 40 yards...it was down.
I think I will be going back to my expandibles (Shockwave...VERY long head when open, and an ENTRANCE wound you could stick 5 finger tips into). I just will NOT go through that blood trailing nightmare again if there is ANYTHING I can do about it.
BTW, They DO fly PERFECTLY. My shot at 31 yards was right on the pin! I SHOULD have an 8 point rack on the wall....not guilt in my gut.