Hi,

attached you'll find a pdf file showing the elusive vertical white-space 
errors
using the engraved source block export backend that I demonstrated 
yesterday
evening.

I also attached the org demonstration file and the mini-library that 
makes the
demonstration file work.

You can find also everything at https://github.com/gav451/org-exp-exp
(except for the pdf).

I checked that the errors are also present in a minimal "clean" 
environment
where the only installed packages are engrave-faces, auctex, and 
pdf-tools.

I have also seen these kind of errors on Gentoo systems, but I have no 
access
to those anymore.

I have a patch which is unacceptable because it limits the font size to
"normalsize" and it requires visible draw boxes around floating 
listings.
Nevertheless, I attach it to show where I got stuck.

Regards -- Gerard