I just got home and wanted to see wether I had a call on my iPhone and pressed the 'wake up' button - and nothign happened. First I got somewhat nervous but then I just put the cable con and the screen came on completely normal, the phone was always running, it just didn't wake up when you press the button. And it stayed that way. everything looked normal, it just didn't react to the wake up button.
I then thought maybe it's better to do a complete restore (dfu mode) with the pwned ipsw file, but that didn't work (error 1600). I then just tried an original ipsw and that seems to work, the phone is restoring right now. There has to be some difference between the modified and the original file!