Now do that test while casting a spell. Yeah classes with instant cast abilities do not have the problem as often(except elusive jump/brd jump back) but they will have it when they use something with a long animation while moving at the same time. If you are not using abilities you will never see this problem and if you play this game like its FFXI and don't worry about utilizing every millisecond of the GCD you will rarely see this problem. Auto attack updates your position after a ability so melee and brds will have this problem a whole lot less then casters. It is not lag it is a bug where GCD/animations are causing your position to not update properly to the server.