Whenever you select a new target, your client sends a msg to the server with the name of your new target, which in turn sends it to everyone in your group. If your latency is about 250ms, then that means it's going to take about half a second or so before the person following you knows what your new target is.

So, to compensate, whenever you select a new target, just wait half a sec or so before pressing your cast button. Kinda sucks, but you can use it to your advantage sometimes once you get the hang of it.