if it has "orders" that vague, would showing obvious enough dismay that Jean doesn't accept his agreement to them be "refusing"? In a situation where he is aware that having those tells caused him to get out of the order

I envision that as part of the ramping-up: the magic, as it grows out of control, starts actively reacting to anything Kaeya does to evade Jean's orders. Enforcing less and less explicit orders over time comes hand-in-hand with shutting down each new way Kaeya finds to work around them.

In fact, the cause-and-effect might even be the other way around! I'm tempted towards the notion that aside from the issue of a Vision's power being way more than the spell needs (and the Pyro-on-Cryo complications), the fact that a Vision responds to the intentions of their bearer is also playing into this. At the time Diluc does this magic he is still reeling from the revelation that Kaeya was deceiving him for all those years, and afraid on some level that he's going to somehow be able to wriggle out of this safeguard by fooling Jean as well. He does not want Kaeya to find any loopholes! And if I go with that, then the spell, turned by the Vision into an active rather than passive restraint, closes said loopholes as soon as Kaeya finds them--each strategy, including that one, has only a limited window before the magic starts triggering on it. And if that's what's happening, then forcing indirect or non-orders is just part of that overgrowth, because 'she didn't make it a direct order' is just another loophole, as far as that nasty mess of Abyssal magic and Vision power and Diluc's mistrust is concerned.

Even if that's not the specific mechanism I go with for why, I do know the magic is shutting down even that kind of passive resistance. The incident that makes Kaeya decide he has to tamper with it involves him being completely unable to give Jean mission-relevant information because it would have changed her strategy and the magic takes that as 'arguing' even though she would want to know. People get hurt because of it (including him)! No one gets killed this time, but... it's worth the risk to him not to put Jean in the position of being unwittingly responsible for someone's death. Because Diluc's coming home someday, and there's "so uh we might have anchored this on you without your knowledge or consent," and then there's "so uh someone died because we anchored this on you without your knowledge or consent," and there's both a moral event horizon here and, on the personal level, only so much forgiveness they can beg.