Guild Wars 2

So, a couple minutes ago in WvW I got moa’d by a mesmer when I had been in stealth for longer than it’s cast time. Then in another instance another thief perfectly follows a rather complicated evasive pattern for a full 10 seconds of stealth, hitting me with his auto.

Has the mechanical implementation changed somehow?

The moa thing has to do with the fact that the cast started before you stealthed.
A player following you while you’re stealthed by using auto attacks is simply a good player. If you hit a stealthed target, the AA chain continues which allows any class to track you really.
It’s pretty basic stuff

Thanks for the response, but moa’s cast time is 1 second, not 4-5. Also the thief was constantly turning to face my change in direction.

Are you sure it was a mesmer that polymorphed you? With the June 23rd patch engineers gained the ability to toss Elixir X which is a ground-targeted moa morph which would hit you regardless of whether or not they could see you.