Not the most satisfying answer, but at least it has now sunk in why it is the way it is.
Re. “expectations”, there are expectations from the point of view of knowing what the code does which we both understand, but also some user expectations that are implicit in my user base (POLS - Principle of Least Surprise). If they observe that looking up a term by itself, & also that term with a rank filter, they get the expected result, they then come to expect that looking up AOU codes reliably returns the expected result, not from an understanding that it was coded that way, but from empirical evidence. When they then apply a taxon filter to that term and see it return the “wrong” result, this will be hard to explain. I suppose I could print a disclaimer at the bottom of the output in fine print like “Not seeing the result you expected? Try removing your taxon filter.” but I’d hate to have to do that.
I agree with you that this is not the bug I thought it was, so that brings us back to why I can’t use autocomplete (no taxon filter) and so the logical next step for me is to file a feature request for that.
Thanks for bearing with me, and for the explanation.
Ben