How I can open xml file in infopath form programatically?H

Hi! I have a xml file that I need to open in infopath form.

I do it in the following way:

                    XmlDocument xmlDoc = new XmlDocument();
                    xmlDoc.Load("C:\filetopen.xml");

                    XPathNavigator root = MainDataSource.CreateNavigator().SelectSingleNode("/ns2:root", NamespaceManager);
                    root.OuterXml = xmlDoc.OuterXml;

And it works.But, I have 5 different forms that have own xml files. In 4 of them everything works fine as expected.

But in one form only some part of data is displayed, another is missing (and I dont get any errors).

I have some rules that overwrite some data from xml file. And these rules exist in all forms, because I need them.

And these rules should work only when something happens (value is changed etc). 

My question.. why it works in all forms except this one? What do I miss? What should I do to make it work?