[cups] CUPS classes wrecking printing

[Gary Dale]

I've running Debian/Bookworm (stable) on an AMD64 system - a laptop. 
It's a fresh install of Debian from about 6 months back that has been 
kept up to date.

Each December I am involved in an event that requires me to use 3 
photo-printers to print a lot of 4x6 photos. It takes 2 or 3 printers to 
get the throughput so people aren't waiting for their photos.

I've been doing this for a decade using various photo printers. I've 
always just set up a CUPS "photo" class and added the printers to it. 
Then I'd use lpr -P photo <name of jpeg photo to print> to send the 
output to whichever printer was free. I even did it last year using the 
same laptop and printers and things worked.

This year, because it was a new OS install, I had to connect the 
printers and install them again. This required the gutenprint drivers 
for two of the printers while the newest seems to work "driverless".

All the printers were tested individually and printed the CUPS test page 
perfectly.

However when I sent something to the "photo" class, whichever printer 
received the job just printed a page of bands of colour. I could send a 
picture to an individual printer OK but not send it to the "photo" class.

I got through the event by skipping the lpr -P photo... command and 
manually selecting a printer from Gwenview when I was viewing the 
picture earlier in the workflow (to verify it was worth printing). This 
was not ideal and I only got through it because this year's event was 
less than half its usual size.

This was not an lpr problem because I also couldn't print to the class 
from Gwenview. CUPS classes seem to be broken.