Can you check that [Calculated Eval Due] is a correctly formatted date?
The simplest way is to add the field to a listbox and see if the values are shown as dates or numbers, and whether the data is left or right justified.
If shown as a date, but right justified, the value is correctly held as a dual field and will match the data returned by today()
If shown as a date but left justified, then the value is held as text and you will need to use something like
Date(date#([Calculated Eval Due], 'DD/MM/YYYY'))
replacing DD/MM/YYYY with your actual date format to convert the data to a correct date value.
If shown as a number then date([Calculated Eval Due]) should convert the data to a correct date format.