Without any checks, my first thing would be, to check in both computers if any of the executables related to cups might have different rights settings.
Especially the executable, which creates the file in /tmp. A file which is created mostly gets the ownership and posessions of the creatorbinary (father- child-principle). The other thing, which maybe show more informations: If you are able to print from the commandline, then "strace" might be a good help, just to see, when and wo´ho is creating the tempfile. As you have one working system and another "alien" working system, you might be able to compare both things and find the different behaviour and step, when it happens. Maybe so you get more data, to get closer to the cause. Yeah, maybe help not much, but so I would do. Best Hans
