Silly question, but on my pre-'74 AMCs, you press the lock button and then you have two choices. Either:

a) with the door open, pull the interior handle - then release. Close the door. Door remains locked.

b) with the door open, hold the exterior paddle OUT and shut the door. Door will remain locked.

Is that not the case with the Barracuda? I remember my '68 New Yorker was pretty much the same. Lock the door, pull the interior handle, close the door.