OK. I've found something which may help.
I uninstalled the drivers and hotplug:
sudo make uninstall
Then reinstalled the drivers with
sudo make install
and did not
sudo make install-hotplug
I then mounted my Kubuntu 11.10 partition, and went to
on that partition. Then, as per this thread
I ran this:
cat sihp1020.dl > /dev/usb/lp0
and the printer works as expected. Does this maybe give you an idea what has changed in Kubuntu 12.04?
I will make a little script to do this, and run it when I need to use the printer, so it's not really an issue anymore.