The remote forces the BECM and engine computer to exchange a fresh set of scrambled security codes. You (and Disco owners) can avoid this problem by unplugging the hood alarm switch (you have insurance) or by holding it down when jumping off. The moment the battery is jumped, the sleeping alarm gets a jolt of power, awakens to find a door open, and immobilizes the vehicle. Kinda like kicking the chair of a sleeping deputy holding a shotgun.

 

Happened to my P38 as well once. I was stuck in one of the ghetto parts of town and everyone is watching thinking why is this guy trying to steal a Range Rover when the alarm is going off and there's so many people? Haha but I believe some people call it 'superlock' and there's a sequence of unlocking/locking to relieve it. If I remember correctly, put the key in the door and turn to unlock and hold for 3 seconds, lock and hold for 3 seconds, unlock and hold for 3 seconds and the parking lights should light up and all the locks should pop up and viola you no longer have a disabled engine or a loud alarm in your ear.