You'll need to be more specific as to what is happening. So you opened up the Settings menu while you were reversing and left the Settings menu open? Yes, this will block the rear view camera and is normal operation.
Certain operations will close the rear view camera "window". For example, if you use the voice command for navigating, this will close the rear camera.
In my BMW, if I hit the menu button while reversing, the rear camera disappears. I have to hit the camera button again to view it.
There are two rear camera ON modes:
1) Full Screen, top half is camera, bottom is ultrasonic
2) "App" window, this is about 1/3 the screen, and will sometimes close when you launch another app.
Mode #1 is what R gear is supposed to present. You can close it if you like in the upper left X.
Mode #2 can be activated in any gear.
If it will let you.
If you park the car in Mode #2, then Mode #2 will present next time you drive it. However, if you launch another app that closes #2, a voice command will not necessarily launch it. Shifting to Park or stopping won't fix it.
So for some people like me, who use the rear camera in #2 while driving, I have to remember to close the #2 window manually before parking, otherwise, there is a big risk you will not be able to put into either Mode #1 or #2 easily.
If BMW has the same problem, I haven't seen yet. GM, Ford, Audi, MB, JLR, Hyundai don't have this problem. When you shift them into reverse, it always defaults into rear camera mode at first. You must deliberately close it to make it go away in reverse.
I'll post a video I took of it soon. It's a bug not a feature. When you first enter the car, and put it in R, it should ALWAYS present the Rear Camera to start with.