We are having the same issue except on our Vendor files.  We have the default at the Vendor file coded for "Due Upon Receipt" yet when creating a new bill, it sets the due date at Net 30 and leaves the "Terms" field blank.  

From my previous experiences with customer support, the response suggested by QuickBooks is the same "canned" answer to all issues when they have no idea how to resolve - Backup and Rebuild.  Good luck getting a response as I have NEVER received any resolution to issues we have reported.  We get the "We have forwarded to our engineers . . ." and then never see an update or find a solution.