Not sure about the screw, but as for the unlocking, I have experienced this before (more than once) it is a strange phenomena.
I think you'll find that if you open the car with the key, the alarm will sound, start the engine straight away, the alarm will continue to sound for another 10 secs or so then it will stop.
Move your car down the road or into the next street, get out and try locking and unlocking and it should be fine.
The only "explination" is interference ?? The car thinks its being tampered with and shuts itself off.
Hope this helps.