Document scanner Panasonic KV-N1058X: Wrong image height

It was one of my bigger mistakes that I bought a Panasonic KV-N1058X a few months ago. I am having all sorts of problems with it, but yesterday I noticed something that stopped me immediately from using it further: It shrinks all images by a certain factor along the height axis. I am living in Europe where written materials mostly are of DIN A4 size, which is 210 mm x 297 mm. The scanner is configured for 600 dpi, so this would mean 4961 pixels x 7015 pixels. I have taken a sheet of DIN A4 paper and have verified that it was perfectly rectangular and had exactly the dimensions mentioned above.

Question by Binarus on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.