This is the Infocom problem: You're trying to present the user with two fundamental illusions. 1) the computer can understand what you're saying, totally and completely, and 2) that you (or it) can do anything.

However, it can't, it can't, and you can't. And when the illusion fails, it's frustrating: Neil Stephenson would call it Metaphor Shear, I (being less fancy) would call it why-didn't-they-give-me-a-better-ui-or-at-least-a-manual-dang-it.

This is ultimately why I prefer unambiguous interfaces over "friendly" ones.