GM Service Manual Online
For 1990-2009 cars only

If the power door lock switch is pressed when the key is in the ignition and a door is open, all the doors will lock and only the driver door will unlock. If the doors are closed, they can be locked by using the Remote Keyless Entry (RKE) transmitter. Be sure to remove the key from the ignition when locking your vehicle.

This feature can be overridden by pressing the lock button on the RKE transmitter or by pressing the power lock switch a second time.