I know its been talked about in other posts, but after quick glance I haven't seen anything about it posted in accepted bugs, and had it happen to me.
I find it hard to believe that it is intended that the combat log shows a heal of 1439, then take a hit of 592... then a little later die.
http://imageshack.us/a/img196/9494/d5vo.png
Im noob at pictures on the interwebs, hopefully its readable
I've also noticed esuna being used on someone requires a bit of delay... I don't know how many times when I stated doing AK that I'd try to precast esuna as Last boss was casting it's disease. The tank gets +disease. Esuna hits, and says has no effect, tank still has disease.
Is it game breaking? No.. but it's certainly annoying, and imo not really acceptable in a modern MMO.
Thank you Nooblet for your post outlining the trouble you are having with dying after taking seemingly non fatal damage, this indeed sounds like a bug.
In order for me to submit your report, I will need some more information. You can go Here and you can find templates for Windows and PS3 that represent the kind of details we need. Once you can provide such information we can move forward and resolve this issue. For now I am going to move this thread into Insufficient Information. You will not be able to reply, so once you have gathered the requested data please create a new bug report thread.