Tip to those buggies that have both short and long arm setup possibilities like the MP9 and THE Car White Edition. When you go to short or long arm change the upper link length to maintain proper camber gain. With the shorter rear arms on the MBX7, the rear upper links were very long(the point were the link attaches on the rear shock tower is inwards than the lower inner hinge pin) causing a very aggressive rear end with low traction. Drivers didn't adjusted the upper link length because they have hardwired that a long upper link always equals more traction. Something like this happens with the MP9, drivers complaining of not enough steering. Move the rear upper link one hole up on the shock tower and see if you now have more steering.
The rear upper link angle is a powerful adjustment, use it and learn what it does to you and your buggy.