Unable to set "column settings" of Yes/No (Check Box) values "Required, Optional, Hidden" of content type column

Hi, SharePoint 2010 and I have created a number of site columns of type Yes/No (check box). I have created a number of content types and used these column types but when I try to change the column setting within the content type to "Required, Optional or Hidden" I am unable as the settings are greyed out and I am unable to change them.

Even in the Parent content type I am unable to change this particular type of column value so it isn't an inheritence setting as it's the parent content type. Am I doing something wrong?  

Note - I am recreating a list from a SharePoint 2007 site and I am able to change the setting here, have i configured this incorrectly or was this something that could be done in SP 2007 but not SP 2010.

Thanks fo any help.