I do not think that is an issue with SoapUI tools, instead it depends on the application you are working with. Some applications support either json, or xml or both some cases. And that when you see different behaviours by different people as each of you looking at different application.
For clarification, you can contact your application development team and see whether you need to expect the response in which format(json/xml or both).
I dont think its problem with Application code.Because for the same application code,JSON response is shown as XML in XML view in 5.0.0 and showing as only JSON in 5.2.0
