If you FD and get up instantly, mobs will just evade if it's not a resist, but if you keep laying in FD sometimes they will just keep attacking as if you didn't even use FD.. Didn't really understand if this is your issue, but yeah, don't stay under FD when you used it, it's much safer to FD outside of mob's original position aggro range and get up instantly after using the spell.. That's how it is from my experience at least. It's probably bug since on any other server I played you could safely keep laying in FD, but here not really.