Maybe I'm missing something.
Why should the vehicle's temperature profile have anything to do with its dynamical behavior? Are they implying that changes in heat cause volatiles to escape, causing thrust? Or is it that fluctuations in temperature somehow modulate the telemetry?
Although it still may be too early to rush an amendment to Einstein, this effect certainly bears follow-up (it's chilling to know the old telemetry was almost discarded, no doubt as a cost-cutting measure). This is the Pioneer Anomaly, have similar effects been noted with the Voyager spacecraft?