I believe your issue is down to the fact that your radio button is in a listivew. When you refresh the dataview the whole list gets refreshed and then the focus on the radio button is lost. What you really want is for new objects to be added to the list but not the whole list to be refreshed.
Are you using the radio button widget from the appstore or the standard radio button that comes with the platform? I consistently use my keyboard only in Mendix and I have never experienced any problems with keyboard accessibility.
The appstore widget is not fully accessible, to many (unnamed) elements so accessibility tools get confused. The widget is on github too, so you could look into improving the structure there: https://github.com/mendix/RadiobuttonList