Only the top 15% of the screen works?

Hello my Ifixit friends! I have the WEIRDEST problem I've ever had with a phone.

Customer dropped and broke the screen on her S4. When replacing the screen, the following happend;

Samsung Galaxy S4 (GT-19505)

When I star the phone, I get the Samsung Symbol whirling around. If the battery is low, I see the entire battery symbol towards the bottom of the screen.

However. When I get through the Samsung logos etc to the "desktop" I only get the top 15% of the screen. After a while a collegue and I quickly realized the screen we are seeing is the screen that would normally show if you had a "S-View" backside on. With the little see through window at the top.

This phone has a normal backside on, however.

We tried putting on a S-View cover on, and then removing it however the screen stays the same.

When we did a total reset on the phone we see the entire screen, from top to bottom. However. As soon as we go back into the normal booting and get to the "desktop" the problem remains.

Some very knowledgable person knows how the case works together with the phone? I know it works with magnets, but where/how do they interact? Could help me locate the problem. :)

Thanks for all the help!

/EDIT Due to archving.. Not enough info? I've written a book here! :)

/EDIT#2 Due to archiving.