It is believed that CZAR52 increased bank as to not fly over the restricted area. So halfway during the turn, the pilot increased bank and simply stalled the aircraft.
Here is a picture I found from wiki who also reports the same findings. I'm not sure what the actual final USAF report found. However, I believe it was strictly pilot error and not an aerodynamic problem with the buff.
For most aicraft pulling closed, the turn radius would have taken them outside the restricted area, and would not have been a factor.