I don't know Polygon. I know my 93 LeBaron convertible (base model with lots of options I guess) and my friend's 91 Dodge Dynasty both have this feature. If you open the driver's door while the key is in the ignition, and you press the power lock button, on either door, to *lock* the doors, it won't function, however you can still unlock them with the power lock button. I don't know much about this feature other than what I just typed, but I was assuming it was an EEK thing. However, you say you have an 89, which would mean you have the 80's boxy interior style. Perhaps this feature came out with the 90s "organic" interior style. Then again, the Dynasty never recieved an interior facelift... hmm a very good question you have asked... I am confuzzled.
BTW dpaswill, your problem sounds identical to what happened when the IOD fuse burned out on my Baron.