MSP430F2619S-HT: Decreasing ADC Resolution as Temperature Increases

Tool/software:

I'm seeing some very strange behaviour of the internal ADCs on the MSP430F2619S-HT over (around) 100 degrees C.

This part is supposed to work up to 150 degrees C according to the data sheet.

Basically the ADCs return values with less and less resolution, i.e. the LSBs are disappearing as the temperature increases.

Any ideas?