When using apps as a second user, why do new screens within apps open behind the main window?
I did resolve this issue eventually. I use App Protector Pro on the main account of the device, but it is not installed in the second user. Somehow having this enabled on the primary account disrupts the screen ordering on the second and subsequent users. It occurred to me that this might be the case, and testing has proved it so. 

You need to disable App Protector Pro to resolve.