How do I tell my Costs/Expenses not to Combine on the Invoice?

This is controlled by the Client Advance/Expense Code itself.  In File Maintenance Manager, click on Tools, Manage Codes and select either the Expenses or Client Advances from the drop-down.  Select the Code you want to stop combining on the Invoice and remove the check mark from the Combine option. 

Note: You can return the Client Advance/Expense Code to combining by replacing the check mark back in the Combine option for the Code.