Custom body field not storing

I recently updated code from 2008_2 to 2013_1. One of things this code does is add new SalesOrder records with custom body fields. All is working well except a couple of the custom body fields aren't being stored.

I confirmed that my code is correctly looking up all of the custom body field internalIds, creating the SelectCustomFieldRef and StringCustomFieldRefs, and adding them to the CustomFieldList on the sales order record. There are 5 fields in the list: 3 Free-form Text, 1 Hyperlink, and 1 List/Record. The Hyperlink and one Free-form Text field are not stored.

After I added the sales order record, I immediately looked up the record from the BaseRef in the WriteResponse.  There were 8 custom body fields. 3 of them were values I passed in. My 2 missing fields aren't in the list at all. There are no warnings or errors regarding custom fields in the WriteResponse.