When you edit the default values of a repeating section, they always get repeated for any other instance that is inserted.
Instead of using Default Values to set the node values, you can use code or Rules. If you are just setting the value of nodes that are already present in the form when it is open, then you can use Rules, but if you need to insert nodes into the XML, then you will have to use code.
For Rules, use XPath such as node[1] = 'one', node[2] = 'two', etc.
For code, use the insertAfter() or appendChild() methods on IXMLDOMNode.
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge