Word is compressing images even though "Do not compress images in file" is selected - why?

I have a document in Word 2013 and I’ve inserted some very high-resolution JPG images (line drawings). When I print to PDF, they look fine. However, as soon as I save the file and reopen it, the drawings are very obviously down-sampled — the line drawings look choppy and dashed.

As noted in the question, Do not compress images in file is selected. I’ve also set the default output to 220dpi, but that shouldn’t matter because I’ve asked it not to compress. (In any case, 220dpi is not good enough for me – I need this to be a high-quality print.)

I’ve verified & re-verified the settings, tried many convolutions, and reinserted the original pictures more times than I can count.

What could be causing this to happen? Is there some other option I am missing?