A variant that does make sense and is a real concern is that as the AGI learns, it could change its definitions in unpredictable ways. Peter De Blanc talks about this here. This could lead to part of the utility function becoming undefined or to the machine valuing things that we never intended it to value - basically it makes the utility function unstable under the conditions you describe. The intuition is roughly that if you define a human in one way, according to what we currently know about physics, some new discovery made available to the AI might result in it redefining humans in new terms and no longer having them as a part of its utility function. Whatever the utility function describes is now separate from how humans appear to it.

That's what I basically meant.