If I'm not mistaken, one of the features of some car alarms is an anti-towing device that disables the ignition when the "tilt" mechanism has been activated.
It's the only thing I can think of at the moment, maybe check the literature on your alarm to see if this is correct. It wouldn't make sense that the car would start after it was leveled out. Maybe the switch clears itself, but what good is that? What happens if you park it on a steep incline?????