When joining screen and frame, LCD turns off but backlight stays on?

Hello,

I was repairing an iPhone 5 today. When I joined everything together I tested the screen and everything looked fine. I then left the screen turned on, but when I start putting the screen in the frame to secure it, the LCD image suddenly disappears but the backlight stays on. Turning the phone on/off still works at that point so it's a screen related issue I think.

When I lift the screen up again, and press the power button twice to go in and out of stand-by, the screen works again, and I can reproduce the above process.

I don't know what to do, as soon as I try to put the phone together, the LCD image stops working! Is my screen faulty?

Is this a known problem? I can't seem to find it on Google.

Willem.