Okay, I had absolutely believed that I had tried making the call to my savePos() function to try to diagnose whether the signal had something to do with it, yet when I disable the connect()ion altogether and call it explicitly, now these APIs want to behave like good little children and do what they're supposed to. So, essentially I shot myself in the foot by handling this with modelAboutToBeReset(), which implicitly trashes the internal cache of visible indexes. D'oh! Argh, etc. Thanks for the help, folks.

@Touchoco Glad it works, but it's a shame to have to change over to 32-bit Qt app just to be able to talk ODBC to Excel. If you want to pursue this further I think it is a non-Qt issue. You would have to Google for something about how to ODBC from a 64-bit executable when I have such-and-such (probably 32-bit) Excel, or similar.