How can that be normal? He clearly states the image size shrinks, not the page size as would be expected. I saw that happen a few times but is quite random on my system, 90% of the times it doesn't happen but sometimes it does. When it happens I usually quit the program and when I get back it usually works fine.
Look at the top of his preview panel in his shots.
The page size says 78.34 inches in one and 39.0 in the other.
What is odd, and I don't think we have all the facts is that one screen shot is showing 600 x 600 PPI for input resolution and the other shot shows 300 x 300.
The print size will shrink if the first print size was something like Fit to Page, or one dimension at was at max size.
Try it. Simple try without even using roll paper.
Set 8.5 x 11 paper with print size as Fit to paper.
Then simply change paper size in driver to 8 x 10 paper.
The print shrinks too.
The image never shrinks unless you change resolution of the image.
Fred