Is stealth broken?
This is a known issue, also referred to as “perma-stealthed thieves”. ArenaNet are aware of it It’s a rendering issue that started with the last patch, afaik, and I think it will be fixed soon.
Are you completely sure that this is “known” issue. There was a thing few weeks ago where like 90% of the players got unlimited loading screen and some incredibly unintelligent customer support dude thought it was not an issue.
Lets make it clear. It is an issue and it takes no more than 10 minutes in PvP in order to be seen in action. In rare occasions you can be downed without seeing the thief killing you at all (talking 4-5 hits, not glass cannon build). When mesmers disappear is whole another disaster because of chaotic clones and fancy effects (yay). Also there are some thieves that disappear for huge amount of time and man can’t tell whether or not this is a bug or a feature.
This is huge issue. At least give us an ETA or something. I know that the game is full of bugs and that the sPvP is the least of your concerns, but please, this one is important. I hope you see that.