Is there any way to rotate the perspective or object while selecting corners or lines using RoundCorner? When working with complex shapes I often need to select multiple areas that are not visible from the current perspective. Unfortunately, any attempt to pan, move, rotate causes the selection process to stop. And, it is not always possible to apply the geometry separately without unexpected or undesired curves appearing.
Are you using the center mouse wheel to navigate in the model? If so, you should be able to orbit, pan, and zoom without any problem. Otherwise you can preselect the edges before calling Round Corner.