Greetings,

I'll check with my nephew who has a '99 Grand Vitara and see if his exhibits
the same behavior.  However, my wife's Kia Sorento will automatically
re-lock if you unlock it with the remote but don't open any doors in about
20-30 seconds.  It only behaves that way if you use the remote to unlock it
and was designed to relock if you accidently unlocked it without realizing
it while walking away from the vehicle.

My 2004 Chevy 2500HD operates in a unique way as well.  If you activate the
power locks either by the remote or by a door switch while a door is open, a
chime will ring but the doors will not lock until 5 seconds after the last
door is closed.  If you hit either button a second time all the doors will
lock regardless.  But if the doors are all closed and you hit either button
the first time all the doors will lock without the delay.

Cheers - Jonathan