I have custom fields that I created for sales order and invoices for items. In items this one custom field, called SC, has a Yes or No multiple choice. I did not check, "Allow users, to enter their own text will not be saved to the list". 

I never had this checked and I don't for other fields. Yesterday I add a 3rd choice to the Yes and No for this SC field. After that when a user tried to enter a sales order or create an invoice they would received the warning message below. 

But the SC field was NOT blank and if you tried to choose from the drop down it wouldn't accept it and it would jump down another line. 

The only fix I could find was to check the "Allow Users" in the define fields. I don't understand why I only have to check this for this item and not others that I created.  Maybe something changed with a new update? I have other fields that have a few choices and never had this issue.