What people expect from a person explaining something and how a machine interprets it are two different topics, but are confused with being the same thing. Let me explain. You take it for granted when you converse with someone that in the course of the conversation, you are nodding, gently saying, "Huh?", and so forth. As such, you are communicating to the speaker that you understand or that you need clarification. Machines never get any indication from any additional input that their "output" requires clarification. So they can only operate on static rules.
The interplay between speaker and listener cannot be overlooked or taken for granted. Consider the perceptions you have when you use a search engine. You "believe" that a certain search engine is superior to another. It is only because you know how to make your clarifications quickly through your mouse clicks. Keep in mind that most search engines have some heueristic logic that begins to "learn" from the responses of a searcher. You train your mind to match the responses to your clarifications of that search engine (or speaker) and your perception is that you "understand" the speaker or the search engine "works better" than another one.
Now, as to the shift in pronoun usage, it's final meaning is dependent on your clarification dialog with the speaker and your observation of whether other listeners require clarification. If everyone in the room seems satisfied with a shift in pronoun usage, you may conclude (wrongly) that you no longer need clarification. The speaker moves on, and you are now out of alignment in your perceived understanding. To expect a machine to work all this out on its own, no matter how much brute force you bring to bear on the problem is utter folly.
To prove this, consider performing a machine translation from an ancient religious text to modern English. Some scholars spend their entire lives trying to interpret nuances of meaning from what someone wrote down five thousand years ago on a cuneiform tablet or a hieroglyphic inscription. What was the author trying to say? Since you can't ask any clarifying questions or gestures, your guess is as good as any machine's.
