ORIGINAL: quiksilver
I spined a big 4x4 about 5 years ago at 8 yards, facing directly awaywith a Triska SK 125 gr. head (76# draw - aluminum 29" arrow - KE through the moon).
This was a shot I'd made many times before with fixed heads. This was my first (and last) experience with high-diameter mechanicals.
Well, the arrow was perfectly placed, and penetrated just enough to bury the head of the ferrule in the bone, and crush the entire unit, shearing off two blades entirely, and demolishing the entire head. The deer ran about 10 yards before the arrow fell out, and I got the joy of watching him stroll across a 100 acre field and into another wood plot.
The head looked like you fired it into a concrete wall. Complete failure.
I'm not here to tell anyone how to shoot or what shots to take, but I think we will all agree that a spine shot facing directly away is a very low percentage shot and that hitting the spine directly can destroy many broadheads. While the fact that your broadhead came out looking like you had shot it into a wall should not be dismissed because any broadhead that is well made, fixed, mechanical, whatever should not fail like that. I think that your example shows a combination of a poorly made head and a less than optimal shot selection. That's not to say that you could not make that shot, but losing that deer cannot be attributed solely to the broadhead.
I have used mechanical heads for 15 years and at times have switched to fixed blade heads. I have lost several deer with fixed heads, due to poor shots. I have only lost one deer with a mechanical and that too was a poor shot. This does not mean that one is better than the other, it just means I need to shoot better.