When I process a sale, I am no longer seeing the screen to enter the Warranty, but the Customer Item (OPE) is still being created.
The above screen will usually appear when the product has been set up to use Customer Items.
But, when all of the settings are correct and the screen is still not appearing check Admin / Defaults / Manage Customer Defaults - Invoice Tab. Is the flag ticked to Prompt for Item Details when Posting Invoices?
If this is turned off the Customer Item is still created but the prompt screen is not displayed.