Never mind, I just pulled down the datasheet. UG-LY.

A fellow practically has to build a box just to reprogram it back to the non-thermistat mode. Sheesh.

The datasheet warns that starting a new "write" while a prior one is still active might cause internal corruption, which could make it flip to thermostat mode.

Does the code ever "write" any of the internal EEPROM registers?

Cheers