Why does my iPad recognize "invisible Fingers"?

Servus,

I'm a German student and my English is not the best. Sorry about that but I try!

My iPad 3 fall to the ground. The front panel cracked and the case bend a little bit. So I bought a new front panel and re-bend the case as good as I could! After installing the new front panel for the minutes everything works just fine but on the next days (I was not using the iPad until then) the front panel turns crazy. It recognizes touches without touching it. So I thought that the front panel does not fit exactly and got it out of the iPad again. I worked on the case again and now there shoud not be any metal in the way. I installed the front panel again but the problem is not fixed.

The strange thing is that it works some times and some times do not. For example if I use it, it may works for half an hour absolutely fine and then out of nowhere the "invisible fingers" come back.

Is there anyone who can help me?

Thanks!