Device URI may incorrectly be set to usb://dev/usb/lp0

This bug report is derived from a thread in the support forum of the Swedish LoCo:
http://ubuntu-se.org/phpBB3/viewtopic.php?f=217&t=58953

When you configure a Brother printer while it's connected to an USB port and switched on, the device URI is correctly configured to usb://Brother/[printer's model name], and things work as expected.

If you configure it while the printer is not connected and switched on, the string usb://dev/usb/lp0 is set as some kind of fall-back device URI. With this value the printer won't print anything.

usb://dev/usb/lp0 used to work on previous Ubuntu versions, when CUPS accessed the USB printers with usblp. Today, with the libusb method, usb://dev/usb/lp0 is simply not correct. It still looks like a correct value, and it's anything but obvious to the user that it's not correct and causes the print failure.

IMO a more reasonable behavior would be to submit an error message, telling the user that the configuration could not be completed, and leave the device URI field blank.

I can't tell if this issue is Brother specific, or if it may happen also with printers from other manufacturers.