"Find New Printers" isn't working.

[Alan Mackenzie]

I'm in CUPS's html localhost:631 interface.  I click on "Find New Printers", and CUPS replies with "No printers found".  There is a USB laser printer attached to the system, and it is switched on.

When I run /usr/libexec/cups/backend/usb, I get

    direct usb://Samsung/ML-1450 "Samsung ML-1450" "Samsung ML-1450" "MFG:Samsung;CMD:PCL5E,PCL6;MDL:ML-1450;CLS:PRINTER;" ""

, so the printer is definitely talking to the PC.

My system is an up-to-date Gentoo, running on Linux 3.3.8.  Its kernel currently has CONFIG_USB_PRINTER enabled; to compensate for this, the Gentoo usb "use flag" is disabled for the package "cups".  Reversing the state of these two items doesn't help.

Please help me debug my broken setup, and get CUPS to recognise my printer.

TIA!