iCloud Mail keeps getting unselected in System Preferences
Have a strange occurrence with my iCloud account on both my Mac Mini and MacBook Air, running 10.8.3 but this started under 10.8.2. iCloud Mail keeps getting unchecked in the iCloud pref pane in System Preferences and the account periodically vanishes from Mail. I have watched the Mail icon in System Preferences get unchecked sometimes just seconds after I have checked it. In Mail (Mail.app) when this happens, behavior varies. Sometimes iCloud is gone from Mail.app and the account has to be set up again. Other times the account is still there but instead of showing up in Mail.app preferences it shows up as a generic "icloud.com iMAP" account.
Any ideas? Deleting preference files, certificates, etc.? Signing out of iCloud on both computers and signing back in did not help. I have not tried creating a new user account on the computer and syncing my 10-15 GB of iCloud data over to that account yet.