All of the teams, front-runners in particular, are "working" in this area. All of them. They do so because if they don't, they can't get through and off the turns as well as those who do.
Not all of the cars are inspected for rear-steer compliance post-race. If they were, there would be penalties handed out every week. On occasion, something binds slightly back there, the housing doesn't "return" enough and somebody (who gets inspected) gets caught out of spec.
This situation can be corrected by the application of penalties much more severe than those currently being handed out.