I've had it happen a couple times over the last 20 years . . . not including spine shot deer. In both cases, the deer were not especially large and were very relaxed when the arrow hit. I suspect that it just caught them off-guard and knocked them off blance. In both cases, the deer immediately got back up and took off running, but dropped in less than 100 yards.

The vast majority of my kills featured pass-thrus with the deer blasting away.