I think I should have been more clear above... I couldn't print to any cups printers from the flash applet, neither actual printers nor the cups PDF printer. I was trying to print to PDF from the flash applet at the time I was looking at this issue, but after specifying a default printer in cups, printing to any printer from a flash applet now works, default or not. It doesn't seem to matter which is the default but there has to be a default printer in cups.
I think I should have been more clear above... I couldn't print to any cups printers from the flash applet, neither actual printers nor the cups PDF printer. I was trying to print to PDF from the flash applet at the time I was looking at this issue, but after specifying a default printer in cups, printing to any printer from a flash applet now works, default or not. It doesn't seem to matter which is the default but there has to be a default printer in cups.