You might start with an AI that has an agreeable set of goals. There is no guarantee (I think, other people seem to disagree) that these goals will be the same after some time.
That's what I mean. Since it's not quite human, the goals won't evolve quite the same way. I've seen speculation that doing nothing more than letting a human live for a few centuries would cause evolution to unagreeable goals.
I think, other people seem to disagree
A sufficiently smart AI that has sufficient understanding of its own utility function will take measures to make sure it doesn't change. If it has an implicit utility function and trusts its future self to have a better understanding of it, or if it's being stupid because it's only just smart enough to self-modify, its goals may evolve.
We know it's possible for an AI to have evolving goals because we have evolving goals.
A sufficiently smart AI...
So it's a Goldilocks AI that has stable goals :-) A too-stupid AI might change its goals without really meaning it and a too-smart AI might change its goals because it wouldn't be afraid of change (=trusts its future self).
A stub on a point that's come up recently.
If I owned a paperclip factory, and casually told my foreman to improve efficiency while I'm away, and he planned a takeover of the country, aiming to devote its entire economy to paperclip manufacturing (apart from the armament factories he needed to invade neighbouring countries and steal their iron mines)... then I'd conclude that my foreman was an idiot (or being wilfully idiotic). He obviously had no idea what I meant. And if he misunderstood me so egregiously, he's certainly not a threat: he's unlikely to reason his way out of a paper bag, let alone to any position of power.
If I owned a paperclip factory, and casually programmed my superintelligent AI to improve efficiency while I'm away, and it planned a takeover of the country... then I can't conclude that the AI is an idiot. It is following its programming. Unlike a human that behaved the same way, it probably knows exactly what I meant to program in. It just doesn't care: it follows its programming, not its knowledge about what its programming is "meant" to be (unless we've successfully programmed in "do what I mean", which is basically the whole of the challenge). We can't therefore conclude that it's incompetent, unable to understand human reasoning, or likely to fail.
We can't reason by analogy with humans. When AIs behave like idiot savants with respect to their motivations, we can't deduce that they're idiots.