Just thought I would share my experiences with a printing problem I was having.
QCAD (at least some versions) seems to look at /etc/printcap to populate the printing dialog box.
I have had an issue where the wrong printer was being listed in the print dialog (one that had been deleted) and I couldn’t select the correct printer. I think the problem is that cupsd isn’t updating /etc/printcap.
The fix I found was to look inside /etc/cups/cupsd.conf and find the value of the Printcap entry.
In my install of Ubuntu 8.04 it was “Printcap /var/run/cups/printcap”
I then ran as root
ln -sf /var/run/cups/printcap /etc/printcap
The next time I ran qcad the correct printer was listed in the print dialog