This issue has gotten better. During beta i would say 75% of the time I am out of the red before casting bar completed and still took damage. SE acknowledged this was do to server/client checks. I have had it happen a couple times I noticed still and was not a big deal till happened to me when fighting titan and I was way out of charge line and got knocked off still. These are not due to latency but server checks that I still don't think are quite working correctly.