Hi Wacomonkey, sorry I don't have any other ideas on what might be going wrong. I can't really do an investigation on something that only repros with one specific file without being able to test with it over here.
No worries, Michael. I'm truly impressed and grateful for how much time you've spent on my problem as it is! I'll fiddle around with it and see if I can track down what's happening, and post my results here.