Global fields work the same in both 12 and 13 and that is where I believe your error is. Global fields are global to the user not to the file. Each user maintains their own global fields separate from the other users. Here is a link about global fields :http://help.filemaker.com/app/answers/detail/a_id/3604/~/global-fields%3A-an-overview
If you want this field to always show today's date, make this an unstored calculation field, not a global calculation field.
Or you can use the text tool and the Insert Menu while in Layout mode to insert text on your layout that always shows today's date.