That should be it then. I think you will find that you had clicked on an NPM Interface which is why the Interface Details view was loading. If you were to click on an Interface name from within a NetFlow view youi would have not been allowed a drill down view because it is already set to "none". It can be easy to confuse an Interface Details view in NPM with a NetFlow Interface Details view in NTA. Sounds like you want both to be set to "none".
Hope this helped.
