I do a new post rather than editing the previous one to bump it out since I
maybe have found a solution.
First I checked the good contact between the LCD grouding and the motherboard by putting some piece of paper behind the contactor. But I still had the sensitivity issue.
So I looked more precisely at this lcd grounding component. I find out it also connect to the back of the camera. Since there are different pin to connect to the motherboard and to the camera, and reading some electrics arc could happen between the camera pin and the motherboard metal piece used to do the contact, I used tape to isolate the part of the motherboard where the arcs could land:
http://forums.windowscentral.com/at...20/86572d1415127626-lumia-1520-lcd-ground.jpg
So I just put (plastic) tape on the previous selected area.
The screen scrolling of my 1520 is now really smoother, and I can play Secrets and Treasure without firing bullet in space cause of false touch (that was nearly impossible to finish my daily playtime without having this issue before). I still did not have any issue with the Windows Central app (which happened a lot before) and the scrolling is now as smooth as on my lumia 920).
I'll change the tape for electrical tape next time and will cover more accurately the area, because I did not cover the edges and it could be the source of the really rare sensitivity issue I have now.
I use high sensitivity touchscreen setting and glance background since I did not see any differences while activating them or not.
(Note: since the paper wedge bent my connectors, I was forced to let them in place, but I think it's useless if your connector pins are not bent in the wrong way).
PS: I apologize for my English, I did my best.
EDIT: It lasted 5 days, now the ghost touch is back.