Background image stay & render region updates

Is there a way to render a background, and only a render region can be updating or render in realtime?

Does anyone know? The outside of render region is empty. Is there a way to show the whole background from a previous render?

So, is this a software issue?

I am having the same issue and was wondering if this is a software limitation than would it be possible to address it? It is very hard to judge a small render region without the whole context. Very often you need to compare a change you have done to the current render and this feature seems to be consistent in all of the other renderers and software.