Brown Out Reset not activating at low voltage before code runs wild on PIC24FJ256GB106 (tpoff)

On several PIC24FJ256GB106 parts we are finding that as 3.3 volts drops during power down, the code is running wild before the Brown Out Reset (BOR) becomes active at 2.1 volts and stops code execution. In some cases the code has run wild and ended up run..