Had a 86 7 series that did the same thing, we named it Christeen. I have heard of this a few times, and I am guessing it is a flaw in the Central Locking system. It has a built in "unlock" feature that kicks in on heavy impact or inversion (mercury switch.) I have tested the second feature and it worked quite well! But it seems to have a mind of it's own with the key in the ON position. I have bypassed the CLS and gone to a keyless alarm system, seems to work like a champ.