problem with keys after short period of time

[excogitation]

I recently replaced the housing of my XDA mini,
but now I have the problem that after a while
- I couldn't figure out what exactly triggers it -
the buttons don't work anymore.

If I remove the SD-card sometimes they work again.

I think it might have something to do with the
top 2 screws (antenna cover).

Does anybody know for sure?