Michel, This is a soar subject with the 820. At least in my case. After the screen breaks (which is not that hard to do in the Lumia 820 at least) and you replace it, there is a sort of "digitizing ghosting" that will start happening. It will open apps that you didn't select or zoom in or out. The only thing that gets rid of it (for a little while) is to reboot it.
I've learned to live with it, because I'm not wasting more money on this phone. And although I like Windows, my Nokia experience has pushed me away from it. So as soon as I can or as soon as this one completely fails I'll replace it with a more durable phone. And it may not be a Windows phone, but it will definitively not be a Nokia phone.