CUPS - Store username in Device URI no longer works?

Previously, i.e. OS 10.6.7, you could store a username in the Device URI in /etc/cups/printers.conf as shown below:

smb://username:password@server_name/queue_name

This was quite handy as it meant that users were not prompted to enter a username and password.

However, in OS 10.7 (CUPS 1.5.0) this no longer works and results in:

D [21/Oct/2011:18:44:38 +1100] [Job 23] Backend returned status 1 (failed)

D [21/Oct/2011:18:44:38 +1100] [Job 23] Printer stopped due to backend errors; please consult the error_log file for details.

D [21/Oct/2011:18:44:38 +1100] [Job 23] End of messages

D [21/Oct/2011:18:44:38 +1100] [Job 23] printer-state=5(stopped)

D [21/Oct/2011:18:44:38 +1100] [Job 23] printer-state-message="Invalid printer name"

I'm wondering if there is some CUPS setting I need to change for this to start working again.

Please note: Turning on the Guest Account in Windows is unacceptable as is saving a Username and Password in a Key Chain.