Anti hijack locking

I had to use my spare key today as my missus had run off to the sales with my regular key in her bag.  I thought I was going mad when the anti-hijack kicked in (its set to off normally), but when I got home I did a search and found out that it is key specific - ie it has to be set for both keys in the maxidot. Thought I would remind members of this as it had me stumped for a while!!!