Wrong date in Mail.app and its To-do list: Solution
If you're having trouble entering the right due date for Mail.app's to-do list, or if it's simply not showing the right date label, this solution might help you. Simply check your "Language and Date" preferences under System Preferences, then choose Format tab, and then see if your region selection has a default value (Fixed country name). Custom formats with modified values can cause problems, so better change them carefully.
Thanks to Hooman for the tip!
