Excel changes field format from date to text when date entered.

I have an Excel worksheet that has a variety of formula's and conditional formating in it. There are four different date formated columns in the spreadsheet. When a date is entered into any of the date fields, Excel converts the cell where that date is entered to text and displays the numeric equivalent of the date, e.g. 42401 for february 1, 2016. No matter how we type or entered the date into any cell in the date columns, that cell format changes to text. The remainder of the column continues to show the cells as date formatted shares, HOWEVER, the moment anything is keyed in the cell, Excel changes the cell format to Text.

This has become very frustrating, since we change the cell format back to date, and the numeric value converts to display the date, however, if we re-enter that cell for any reason with the cursor, Excel immediately converts the field format to Text, and when we exit the field, the numberic value is displayed again.