Checkbox 'Require password after sleep or screen saver begins' missing
Both my late 2012 iMac and my late 2011 MacBook Pro 13-inch are encrypted with FileVault2. I know this causes some changes in being not able to automatically login etc. It also changes the password requirements at System Preferences -> Security & Privacy -> General. The strange thing is that on my iMac I can uncheck the 'Require password after sleep or screen saver begins' checkbox, while on my MacBook the checkbox is gone (see screen prints below). On different support communities I saw it's an issue for a while, but I did not find a proper explanation and solution.
Can someone please explain me why the checkbox is gone only on my MacBook and how I can repair it, so I can uncheck this option?
iMac with checkbox
MacBook without checkbox