At this point, not one single native or non-native speaker has ever heard of–let alone agrees with-this tone sandhi exception for “wo3” and “ni3.” I had the teacher clarify the point with colleagues, and I received a short video excerpt with a Chinese speaker saying stuff that seems to have no relation at all to the point at hand. Then, this teacher now says that wo3 and ni3 are only excepted from tone sandhi when they’re the first word in a sentence. as they quite often are. In fact, I have heard people do this–and do it myself–when, for emphasis, that first wo3 is so separated from the following word that you do two third tones in a row because there is no “in a row” feel. When the initial “wo3” is that separated and emphasized, it’s full 3rd tone, never half, which would be weird.
Depressingly, another point came up where the teacher said that the “bu” in a negative potential complement must be 4th tone, not neutral tone as I’ve always been taught. For example, “kan4bu4dong3,” and not “kan4bu5dong3.” Yet the teacher grants that the “de” in positive potential complements (e.g. “kan4de5dong3”) is indeed neutral tone. Then the teacher pulls out a textbook to support the point and shows two grammar points that do not, in fact, address what’s we’re talking about. I pointed out that the third item on that same page says precisely that the “bu” is neutral tone. Teacher reads it and admits the error. How on earth can a native speaker make errors like that? I mean, the erroneous theoretical ideas have to come from somewhere. After that dealbreaker, I’m happy to get what I can from this person’s valuable aspects, as long as I can gracefully evade the inexplicable brain farts. A very nice person with a great attitude for teaching who’s actually not a total dope. The dopey part is just a mystery, and I’m getting a very good rate.