Nice work westfw! That fixes the problem. Thanks.
It would be nice if there was better adherence to a formal versioning system. I should be able to easily compare the commits between avrdude 6.3.0-arduino9 and avrdude 6.3.0-arduino12. Instead, the only tag in the arduino/avrdude-build-script repository is "6.3-arduino", even though there have been 4 separate production releases of avrdude 6.3.0. I assumed the changes made in the avrdude versions included with the Arduino AVR Boards 1.6.20x beta releases would only be the addition of the PB parts definitions to avrdude.conf since that's the only necessary change I would foresee for the toolchain update which was the subject of those beta releases and no other avrdude changes were mentioned.