Opening a new folder and the big picture stays black.

When I start the lightroom, everything works fine. But when I change to a new folder, it doesn't open any pictures in development mode. Instead the big picture stays black. All thumbnails are visible. I can see the images on library also. When I close the program and open it again, then the recently opened folder becomes visible in develop.

In other words, if I want to do work on my pictures I need to close and open the program each time I change folders.

These problems occured after updating to 7.3.1.