There's a spectrum of possible explanation, from "this is a model training artifact which for now they correct via the harness" through to "this is deliberate,

There's a spectrum of possible explanation, from "this is a model training artifact which for now they correct via the harness" through to "this is deliberate, and creates a constantly moving target to make third-party harnesses less efficient for lock-in purposes". I'd not discount the adversarial end of the spectrum.