While testing the car, i had that behavior, the rear breaks grip, while turning hard in corner entry with speed or under braking at last moment a little bit aggressively.To be completely honest some of the slip sensitivity parameters are not ideal, so I will be changing them a little bit for the next release alongside some general tire changes. We also found out in the meanwhile that FINs do not apply aero forces as we though they do, so I will include a corrected side-force modeling. Maybe it can improve some extreme situations.
Although people who have issues with the car as it is will likely not have those issues solved by those changes; it is what it is.