[ubuntu] not asking for password often

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http://ubuntuforums.org – Hi, I have my power setting to turn monitor off after 10 minutes and ask for password to get back in. The machine does not always ask for a password, a bit hit and miss but now it seems to not require a password at all to get back in. It does ask for the password when booting and restarting though. Anyone recognise this issue? Ubuntu 12.10 (Hardware)