Here is an example of a repeatable problem. Let's say you already have a customer named "Patrick James" on your system.

Now create a new lead, and only fill in the Subject line (type anything you like) and fill in the Contact Name as "Patrick".

Save the lead, and then click on the Convert to Opportunity button.

The system proposes by default to create a new opportunity, and link to an existing customer named "Patrick James'. When you change this to "Create a new customer" it still creates the Opportunity with customer name "Patrick James" in stead of creating a new customer.

Anyone has some advice here?