Something is overwriting /etc/cups/printers.conf to require authentication

[Sailorboy]

Binary package hint: cups

I am running cups 1.3.9-2ubuntu7 on my laptop and trying to print to a Samba server. This was working before the latest update, although there was a similar issue in an earlier version. When I try to print I sometimes get a messagebox asking for authentication details. I always see my print job 'held for authentication'. I notice that /etc/printers.conf has the following line added after a print attempt, even if I comment it out before the attempt;
AuthInfoRequired username,password

Here is my /var/log/cups/error_log for the time

E [03/Mar/2009:18:12:21 +1100] Print-Job: Unauthorized
E [03/Mar/2009:18:12:21 +1100] [Job 62] Session setup failed: NT_STATUS_LOGON_FAILURE
E [03/Mar/2009:18:12:21 +1100] [Job 62] Session setup failed: NT_STATUS_LOGON_FAILURE
E [03/Mar/2009:18:12:21 +1100] [Job 62] Session setup failed: NT_STATUS_LOGON_FAILURE
E [03/Mar/2009:18:12:21 +1100] [Job 62] NT_STATUS_ACCESS_DENIED opening remote spool D___Branch_FSM___Feb_2009
E [03/Mar/2009:18:12:22 +1100] PID 18453 (/usr/lib/cups/backend/smb) stopped with status 2!

[Sailorboy (rockell)]

I think this is very similar to 283811 - although the fix described in that bug didn't help me.

My printer is working now but my workaround was to require authentication and delete / re-add the printer with authentication details.