Peter, thanks for forcing me to have a closer look into this. It’s actually a bit more complicated, and I remembered that I already had this “problem” in a slightly different context.
If the error appears depends on the actual image dimensions and on the actual resolution. But the calculation for the error threshold is quite simple: resize height ≥ image height/(image resolution/72).
That’s why it works as expected with the “normalizing” actions from my post above.
I’ve sent you a mail with a minimal macro and a couple of test images in different resolutions. Instructions in the mail.
I leave it up to you if this is a “bug” or “non-intuitive behavior” 