I'm not actually sending a .png file directly, I'm using the Qt library interface to paint an image on a printer device. What that does internally, I have no idea, but it clearly does something different than gimp. If I copy my margin values from the definition I have setup for the kewpie program into gimp's print... dialog (telling it first to ignore predefined margins), then gimp can print a perfectly centered image on the DVD just like I used to be able to do with kewpie (and I wrote kewpie because gimp printing was all messed up and I couldn't get it to set the margins, so we have now come full circle :-).

Here's the attributes of the job kewpie sent to the printer (which did not work):

[root@zooty cups]# python
Python 2.7 (r27:82500, Sep 16 2010, 18:02:00) 
[GCC 4.5.1 20100907 (Red Hat 4.5.1-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cups, pprint
>>> r=cups.IPPRequest()
>>> r.readIO(file("c00052").read)
3
>>> pprint.pprint(r.attributes)
[<cups.IPPAttribute attributes-charset (1:71): ['utf-8']>,
 <cups.IPPAttribute attributes-natural-language (1:72): ['en']>,
 <cups.IPPAttribute printer-uri (2:69): ['ipp://localhost:631/printers/C5500-DVD']>,
 <cups.IPPAttribute job-originating-user-name (2:66): ['tom']>,
 <cups.IPPAttribute job-name (2:66): ['']>,
 <cups.IPPAttribute document-format (2:73): ['application/pdf']>,
 <cups.IPPAttribute media (2:68): ['CDDVD120']>,
 <cups.IPPAttribute job-priority (2:33): [50]>,
 <cups.IPPAttribute job-uuid (2:69): ['urn:uuid:278e3b24-cfd5-3e4b-4678-52822ea1a3e9']>,
 <cups.IPPAttribute output-bin (2:66): ['face-down']>,
 <cups.IPPAttribute output-mode (2:66): ['color']>,
 <cups.IPPAttribute print-quality (2:35): [4]>,
 <cups.IPPAttribute job-originating-host-name (2:66): ['localhost']>,
 <cups.IPPAttribute time-at-creation (2:33): [1304105977]>,
 <cups.IPPAttribute time-at-processing (2:33): [1304105977]>,
 <cups.IPPAttribute time-at-completed (2:33): [1304106019]>,
 <cups.IPPAttribute job-id (2:33): [52]>,
 <cups.IPPAttribute job-state (2:35): [9]>,
 <cups.IPPAttribute job-media-sheets-completed (2:33): [1]>,
 <cups.IPPAttribute job-printer-uri (2:69): ['ipp://zooty:631/printers/C5500-DVD']>,
 <cups.IPPAttribute job-k-octets (2:33): [58]>,
 <cups.IPPAttribute job-hold-until (2:68): ['no-hold']>,
 <cups.IPPAttribute job-sheets (2:66): ['none', 'none']>,
 <cups.IPPAttribute job-printer-state-message (2:65): [u'']>,
 <cups.IPPAttribute job-printer-state-reasons (2:68): ['none']>]
>>> 

And here's the attributes from the job gimp sent (which did work):

[root@zooty cups]# python
Python 2.7 (r27:82500, Sep 16 2010, 18:02:00) 
[GCC 4.5.1 20100907 (Red Hat 4.5.1-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cups, pprint
>>> r=cups.IPPRequest()
>>> r.readIO(file("c00053").read)
3
>>> pprint.pprint(r.attributes)
[<cups.IPPAttribute attributes-charset (1:71): ['utf-8']>,
 <cups.IPPAttribute attributes-natural-language (1:72): ['en']>,
 <cups.IPPAttribute job-originating-user-name (2:66): ['tom']>,
 <cups.IPPAttribute printer-uri (2:69): ['ipp://localhost:631/printers/C5500-DVD']>,
 <cups.IPPAttribute job-name (2:66): ['triangle-118mm.png']>,
 <cups.IPPAttribute OutputMode (2:66): ['Normal']>,
 <cups.IPPAttribute MediaType (2:66): ['CDDVDMedia']>,
 <cups.IPPAttribute job-priority (2:33): [50]>,
 <cups.IPPAttribute InputSlot (2:66): ['CDDVDTray']>,
 <cups.IPPAttribute ColorModel (2:66): ['RGB']>,
 <cups.IPPAttribute number-up (2:33): [1]>,
 <cups.IPPAttribute Duplex (2:66): ['None']>,
 <cups.IPPAttribute PageSize (2:66): ['CDDVD120']>,
 <cups.IPPAttribute job-sheets (2:66): ['none', 'none']>,
 <cups.IPPAttribute document-format (2:73): ['application/postscript']>,
 <cups.IPPAttribute job-uuid (2:69): ['urn:uuid:12ec96f4-fefe-3836-63ca-68add6633426']>,
 <cups.IPPAttribute media (2:68): ['na_letter_8.5x11in']>,
 <cups.IPPAttribute output-bin (2:66): ['face-down']>,
 <cups.IPPAttribute output-mode (2:66): ['color']>,
 <cups.IPPAttribute print-quality (2:35): [4]>,
 <cups.IPPAttribute job-originating-host-name (2:66): ['localhost']>,
 <cups.IPPAttribute time-at-creation (2:33): [1304121952]>,
 <cups.IPPAttribute time-at-processing (2:33): [1304121952]>,
 <cups.IPPAttribute time-at-completed (2:33): [1304122011]>,
 <cups.IPPAttribute job-id (2:33): [53]>,
 <cups.IPPAttribute job-state (2:35): [9]>,
 <cups.IPPAttribute job-media-sheets-completed (2:33): [1]>,
 <cups.IPPAttribute job-printer-uri (2:69): ['ipp://zooty:631/printers/C5500-DVD']>,
 <cups.IPPAttribute job-k-octets (2:33): [20]>,
 <cups.IPPAttribute job-hold-until (2:68): ['no-hold']>,
 <cups.IPPAttribute job-printer-state-message (2:65): [u'']>,
 <cups.IPPAttribute job-printer-state-reasons (2:68): ['none']>]
>>> 

It certainly looks as if gimp is printing the .png file directly and Qt is winding up generating a pdf to send. On the other hand, here's the
attributes from the fedora 13 kewpie spool file (which also worked):

[root@zooty cups]# python
Python 2.7 (r27:82500, Sep 16 2010, 18:02:00) 
[GCC 4.5.1 20100907 (Red Hat 4.5.1-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import cups, pprint
>>> r=cups.IPPRequest()
>>> r.readIO(file("c00087").read)
3
>>> pprint.pprint(r.attributes)
[<cups.IPPAttribute attributes-charset (1:71): ['utf-8']>,
 <cups.IPPAttribute attributes-natural-language (1:72): ['en']>,
 <cups.IPPAttribute printer-uri (2:69): ['ipp://localhost:631/printers/C5500-DVD']>,
 <cups.IPPAttribute job-originating-user-name (2:66): ['tom']>,
 <cups.IPPAttribute job-name (2:66): ['']>,
 <cups.IPPAttribute document-format (2:73): ['application/pdf']>,
 <cups.IPPAttribute media (2:68): ['CDDVD120']>,
 <cups.IPPAttribute job-priority (2:33): [50]>,
 <cups.IPPAttribute job-uuid (2:69): ['urn:uuid:c61131ce-6fbf-3142-7603-0694c8c5572a']>,
 <cups.IPPAttribute job-originating-host-name (2:66): ['localhost']>,
 <cups.IPPAttribute time-at-creation (2:33): [1303654144]>,
 <cups.IPPAttribute time-at-processing (2:33): [1303654144]>,
 <cups.IPPAttribute time-at-completed (2:33): [1303654257]>,
 <cups.IPPAttribute job-id (2:33): [87]>,
 <cups.IPPAttribute job-state (2:35): [9]>,
 <cups.IPPAttribute job-media-sheets-completed (2:33): [1]>,
 <cups.IPPAttribute job-printer-uri (2:69): ['ipp://zooty:631/printers/C5500-DVD']>,
 <cups.IPPAttribute job-k-octets (2:33): [233]>,
 <cups.IPPAttribute job-hold-until (2:68): ['no-hold']>,
 <cups.IPPAttribute job-sheets (2:66): ['none', 'none']>,
 <cups.IPPAttribute job-printer-state-message (2:65): [u'']>,
 <cups.IPPAttribute job-printer-state-reasons (2:68): ['none']>]
>>> 

This also seems to be doing a PDF, and it works on fedora 13.

Anyway, I can clearly print DVDs now using gimp, so there's my work around, but I have no idea what is different with the kewpie program.

One of the things I tried though was setting LD_LIBRARY_PATH to my fedora 13 partition and running the fedora 13 version of kewpie. This used all the same application side libraries as fedora 13, but talked to the cups server running on fedora 14, and that attempt to print with kewpie also failed, so it does look like whatever has gone wrong has gone wrong on the cups side (and it sure acts like the proper printer tray info disappeared on me).

P.S. I also reinstalled the printer from scratch, but the results were identical (though there might have been a ppd update I didn't have, but that made no difference).