It still doesn't seem any insightful to me. Either there is assumption that any sequence of subgoals can be achieved independently of each other or there isn't.

It still doesn't seem any insightful to me. Either there is assumption that any sequence of subgoals can be achieved independently of each other or there isn't. If there is such assumption then... well, I don't know why you even attempted to write a "generic problem-solver" that way, because it obviously isn't the case in the domain where this "anomaly" is presented. If there's no such assumption, then (again, obviously) the problem itself isn't moving something on top of something, but rather to construct a finite (!) sequence of actions, that will satisfy all dependencies between the sub-sequences. "Planning algorithm" whatever it is just cannot start moving things unless it has constructed a complete plan of finite sequence of actions. Sure, sometimes you deliberately write a program that doesn't make tree of all possible outcomes and just "acts" (because efficiency, memory constraints, etc.), but then you know beforehand that your program isn't really solving the problem for sure, it just happens so that your heuristic works. And if it doesn't work — it's a bad heuristic and you know you have to find a better one. You wouldn't be surprised (and wouldn't call it an anomaly, for sure) if an algorithm that always greedily puts a smaller ring on top of next smaller one fails to move a Hanoy tower, would you?